Update shared libraries version info to differentiate against v7.2

Update shared libraries version info to differentiate against v7.2

There some API changes in libgc against v7.2, so the "current" number
of the version info is incremented, thus the version info is now 3:0:1.

There are no API changes in libcord and libgccpp against v7.2
but some implementation changes exist, 2:*:* version info is reserved
for v7.2, so the version info for libcord and libgccpp is now 3:0:2.

* Makefile.am (LIBGC_VER_INFO): Change version info to 3:0:1.
* Makefile.am (LIBGCCPP_VER_INFO): Change version info to 3:0:2.
* cord/cord.am (LIBCORD_VER_INFO): Likewise.