[ekiga] Check for ptlib expat support during configure

[Eugen Dedu <ededu src gnome org>]

commit e9e4ec981dc4fd66c99e769c201c4404381623d4
Author: Eugen Dedu <Eugen Dedu pu-pm univ-fcomte fr>
Date:   Wed Jul 27 22:14:56 2011 +0200

    Check for ptlib expat support during configure

 configure.ac |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index eefae22..72b358b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -692,6 +692,12 @@ dnl ###########################################################################
 PKG_CHECK_MODULES([PTLIB], [ptlib >= ${PTLIB_REC_VERSION}])
 PKG_CHECK_MODULES([OPAL], [opal >= ${OPAL_REC_VERSION}])
 
+# expat is mandatory for presence (at least)
+PTLIB_EXPAT=`$PKG_CONFIG ptlib --variable=PTLIB_EXPAT`
+if test "x$PTLIB_EXPAT" != "xyes"; then
+  AC_MSG_ERROR([You need ptlib expat support to compile ekiga])
+fi
+
 SUFFIX=
 AC_ARG_ENABLE([opal-debug],
               [AS_HELP_STRING([--enable-opal-debug],[link to debug versions of opal and ptlib (opal_d and ptlib_d) (default is disabled)])],