Improve configure script.

* configure.ac: New option --with-pythondir
(PYTHON_SITE_DIR, PYTHON_EXEC_DIR): New subst variables.
* python/libmu_py/Makefile.am: use pythonexec_LTLIBRARIES,
instead of pythonexec_LTLIBRARIES.
(pythonexecdir): New variable.
* python/mailutils/Makefile.am: use pythonsite_PYTHON,
instead of pkgpython_PYTHON.
(pythonsitedir): New variable.

@@ -1136,6 +1136,18 @@ if test "$status_python" = yes; then
     if test "$status_python" = yes; then
       AC_DEFINE(WITH_PYTHON,1,[Enable Python support])
       MU_LIB_PY='${top_builddir}/python/libmu_py/libmu_py.la'
+      AC_SUBST([PYTHON_SITE_DIR])
+      AC_SUBST([PYTHON_EXEC_DIR])
+      AC_ARG_WITH([pythondir],
+           AC_HELP_STRING([--with-pythondir=DIR],
+                          [Specify the directory to install Python modules to]),
+           [case $withval in
+            /*)  PYTHON_SITE_DIR="${withval}/mailutils"
+	         PYTHON_EXEC_DIR="${withval}/mailutils";;
+            *)   AC_MSG_ERROR([Argument to --with-pythondir must be an absolute directory name]);;
+            esac],
+	   [PYTHON_SITE_DIR='$(pkgpythondir)'
+	    PYTHON_EXEC_DIR='$(pkgpyexecdir)'])
     fi
   fi
 fi

@@ -63,7 +63,8 @@ libmu_py_la_LIBADD = $(PYTHON_LIBS) @MU_COMMON_LIBRARIES@ \
  @MU_AUTHLIBS@\
  ${MU_LIB_MAILUTILS}
 
-pkgpyexec_LTLIBRARIES = c_api.la
-c_api_la_LDFLAGS = -avoid-version -module -rpath $(pkgpyexecdir)
+pythonexecdir=@PYTHON_EXEC_DIR@
+pythonexec_LTLIBRARIES = c_api.la
+c_api_la_LDFLAGS = -avoid-version -module -rpath $(pythonexecdir)
 c_api_la_LIBADD = $(PYTHON_LIBS) ${MU_LIB_PY}
 c_api_la_SOURCES = c_api.c

@@ -17,7 +17,8 @@
 ##   Foundation, Inc.  51 Franklin Street, Fifth Floor, Boston, MA
 ##   02110-1301 USA
 
-pkgpython_PYTHON=\
+pythonsitedir=@PYTHON_SITE_DIR@
+pythonsite_PYTHON=\
  __init__.py \
  error.py \
  address.py \