Add new API checking utility

Add a test script to make sure that (with a few exceptions) only symbols
that start with 'g_' are being exported from our public libraries.

https://bugzilla.gnome.org/show_bug.cgi?id=692029

check-abis.sh

@@ -0,0 +1,23 @@
+#!/bin/sh -e
+
+list_leaked_symbols () {
+	nm -D "$1" | grep ' T ' | cut -f 3 -d ' ' | egrep -v "$2"
+}
+
+check_symbols () {
+	if [ "`list_leaked_symbols "$1" "$2" | wc -l`" -ne 0 ]; then
+		echo File "$1" possibly leaking symbols:
+		list_leaked_symbols "$1" "$2"
+		exit 1
+	fi
+}
+
+allowed="^_init$|^_fini$|^g_"
+allowed_in_libglib="${allowed}|^glib__private__$|^glib_gettext$|^glib_pgettext$|^glib_check_version$"
+allowed_in_libgthread='^_init$|^_fini$|^g_thread_init$|^g_thread_init_with_errorcheck_mutexes$'
+
+check_symbols glib/.libs/libglib-2.0.so "$allowed_in_libglib"
+check_symbols gthread/.libs/libgthread-2.0.so "$allowed_in_libgthread"
+for file in gmodule/.libs/libgmodule-2.0.so gobject/.libs/libgobject-2.0.so gio/.libs/libgio-2.0.so; do
+	check_symbols "$file" "$allowed"
+done