Fix overzealous grep in build system

This prevented 'make mod_callcenter' from working because the 'all' in
'callcenter' was matching.

src/mod/Makefile.am

@@ -39,6 +39,6 @@ mod_com_g729-activate:
 	cd $(switch_builddir)/src/mod/codecs/mod_com_g729 && $(MAKE) $(AM_MAKEFLAGS) activate
 
 .DEFAULT:
-	@if test -z "`echo $@ | grep all`"; then  $(MAKE) $(AM_MAKEFLAGS) $@-all ; else echo Unknown target `echo $@ | sed -e 's|-all||'`; exit 1; fi
+	@if test -z "`echo $@ | grep '\-all$$'`"; then  $(MAKE) $(AM_MAKEFLAGS) $@-all ; else echo Unknown target `echo $@ | sed -e 's|-all||'`; exit 1; fi