Improve configuration options.

* am/enable.m4 (MU_ENABLE_BUILD): Change handling of additional-cond
($4): the --{enable|disable}-build-* argument value overrides it.
This allows to use such configuration shortcuts as:

  --disable-build-clients --enable-build-mail

which will build only mail, but no other client.

* configure.ac: New option --with-dbm can be used to
enable/disable building of all available DBM interfaces.
It can be used in conjunction with implementation-specific
options in the same way as described above, e.g.:

  --without-dbm --with-gdbm

New option --with-mailbindir allows for overriding the installation
directory for mail[x] only.

* mail/Makefile.am (mailbindir): New variable.
(bin_PROGRAMS): Rename to mailbin_PROGRAMS.

@@ -59,30 +59,31 @@ AC_DEFUN([MU_ENABLE_BUILD], [
 	pushdef([mu_cache_var],[mu_cv_enable_build_]translit($1,[+-],[x_]))
 	pushdef([mu_cond],[MU_COND_]mu_upcase)
 
-       	ifelse([$4],,,[if test $4; then])
-	  AC_ARG_ENABLE(build-$1, 
-	                AC_HELP_STRING([--disable-build-]$1,
-		                       [do not build ]$1),
+	AC_ARG_ENABLE(build-$1, 
+	              AC_HELP_STRING([--disable-build-]$1,
+	                             [do not build ]$1),
 	                [
   	  case "${enableval}" in
 		yes) mu_cache_var=yes;;
                 no)  mu_cache_var=no;;
 	        *)   AC_MSG_ERROR([bad value ${enableval} for --disable-$1]) ;;
           esac],
-                      [mu_cache_var=ifelse([$5],,yes,[$5])])
+                      [ifelse([$4],,[mu_cache_var=ifelse([$5],,yes,[$5])],
+		              [if test $4; then
+			         mu_cache_var=yes
+			       else
+			         mu_cache_var=no
+			       fi])])
 
-	  if test "[$]mu_cache_var" = "yes"; then
+	if test "[$]mu_cache_var" = "yes"; then
 		  ifelse([$2],,:,[$2])
 		  ifelse([$6],,,[$6="$[]$6 $1"])
-	  ifelse([$3],,,else
-                 [$3])
-	  fi
-	  if test "[$]mu_cache_var" = "yes"; then
-		AC_DEFINE([MU_BUILD_]mu_upcase,1,[Define this if you build $1])
-          fi
-	ifelse([$4],,,[else
-		mu_cache_var=no
-        fi])
+	ifelse([$3],,,else
+               [$3])
+	fi
+	if test "[$]mu_cache_var" = "yes"; then
+	  AC_DEFINE([MU_BUILD_]mu_upcase,1,[Define this if you build $1])
+        fi
 	  
 	AM_CONDITIONAL(mu_cond,
 	               [test "[$]mu_cache_var" = "yes"])

@@ -358,8 +358,19 @@ AC_SUBST(DBMLIBS)
 AC_SUBST(DBMLIB_DEPENDENCY)
 AC_SUBST(DBMINCLUDES)
 
-enable_dbm=no
+enable_dbm=
 disable_dbm=no
+all_dbm="GDBM BDB TC NDBM"
+
+AC_ARG_WITH([dbm],
+            AC_HELP_STRING([--with-dbm],
+	                   [build DBM support (default yes)]),
+	    [		   
+case "${withval}" in
+  yes) enable_dbm="$all_dbm";;
+  no)  enable_dbm=no;;
+  *)   enable_dbm="$withval" ;;
+esac])
 
 AC_ARG_WITH([gdbm],
             AC_HELP_STRING([--with-gdbm],
@@ -570,8 +581,8 @@ check_dbm_impl() {
   esac
 }
 
-if test "$enable_dbm" = no; then
-  enable_dbm="GDBM BDB TC NDBM"
+if test -z "$enable_dbm"; then
+  enable_dbm=$all_dbm
 fi
 
 for impl in $enable_dbm
@@ -1266,7 +1277,14 @@ MU_ENABLE_BUILD(comsat,,,["$mu_build_servers" = yes],,[server_list])
 
 MU_ENABLE_BUILD(frm,,,["$mu_build_clients" = yes],,[client_list])
 MU_ENABLE_BUILD(maidag,,,["$mu_build_clients" = yes],,[client_list])
+
 MU_ENABLE_BUILD(mail,,,["$mu_build_clients" = yes],,[client_list])
+AC_SUBST([MAILBINDIR],'${bindir}')
+AC_ARG_WITH([mailbindir],
+            [AC_HELP_STRING([--with-mailbindir=DIR],
+	                    [install mail to DIR [[BINDIR]]])],
+            [MAILBINDIR=$withval])
+
 MU_ENABLE_BUILD(sieve,,,["$mu_build_clients" = yes],,[client_list])
 MU_ENABLE_BUILD(messages,,,["$mu_build_clients" = yes],,[client_list])
 MU_ENABLE_BUILD(readmsg,,,["$mu_build_clients" = yes],,[client_list])

@@ -19,7 +19,9 @@ AM_YFLAGS=-vt
 INCLUDES = @MU_APP_COMMON_INCLUDES@ @MU_AUTHINCS@ 
 AM_CFLAGS = -DSITE_MAIL_RC=\"@SITE_MAIL_RC@\"
 
-bin_PROGRAMS = mail
+mailbindir=@MAILBINDIR@
+
+mailbin_PROGRAMS = mail
 
 mail_LDADD = \
  ${MU_APP_LIBRARIES}\