add a -with-preferences-dir configure flag

changelog

@@ -102,6 +102,9 @@ SVN trunk:
  textdomain information, making the messages be displayed in English when
  loading levels (#4454).
  * various bug fixes and code cleanups
+ * added a --with-preferences-dir configure option to allow using a dir
+   different than .wesnoth.  Should allow to use svn and 1.0 on the
+   same machine without triggering spurious cache rebuilds ans such things.
 
 Version 1.0rc1:
  * language and i18n:

configure.ac

@@ -222,6 +222,13 @@ AC_ARG_ENABLE([dummy-locales],
               [dummylocales=$enableval],
               [dummylocales=no])
 
+AC_ARG_WITH([preferences-dir],
+              AS_HELP_STRING([--with-preferences-dir], [use a non-default preferences directory (.wesnoth on unix)]),
+              [prefsdir=$withval
+               AC_SUBST([prefsdir])])
+AM_CONDITIONAL([PREFSDIR], [test x$prefsdir != x])
+
+
 AC_ARG_ENABLE([internal-data],
 		AS_HELP_STRING([--enable-internal-data],
 			[put data inside application: Mac OS X only]),

src/Makefile.am

@@ -566,6 +566,9 @@ if GCC
     CXXFLAGS += -fno-omit-frame-pointer
     CFLAGS += -fno-omit-frame-pointer
 endif
+if PREFSDIR
+    CXXFLAGS += -DPREFERENCES_DIR=\"$(prefsdir)\"
+endif
 
 CXXLD = $(LDPREFIX) $(CXX)