make GST_PLUGIN_LDFLAGS only be flags; GST_LIBS should be added manually to each...

make GST_PLUGIN_LDFLAGS only be flags; GST_LIBS should be added manually to each Makefile.am so we are sure it goes

Original commit message from CVS:
make GST_PLUGIN_LDFLAGS only be flags; GST_LIBS should be
added manually to each Makefile.am so we are sure it goes
*last* and doesn't add -L flags before linking in libs of our
own, like, say, internal .la libs, that then accidentally pick
up the installed copy.