* GUILE-VERSION: move all but guile-readline library versioning

* GUILE-VERSION: move all but guile-readline library versioning
information here.  guile-readline is still standalone.  Bump
CURRENT interfaces to 15 to allow some headroom for 1.6 release at
Thi-Thien's request.

* configure.in: AC_SUBST the centralized shared lib versioning
variables from ./GUILE-VERSION.
(LIBQTHREADS_INTERFACE_CURRENT): new AC_SUBST.
(LIBQTHREADS_INTERFACE_REVISION): new AC_SUBST.
(LIBQTHREADS_INTERFACE_AGE): new AC_SUBST.
(LIBQTHREADS_INTERFACE): new AC_SUBST.
(LIBGUILE_INTERFACE_CURRENT): new AC_SUBST.
(LIBGUILE_INTERFACE_REVISION): new AC_SUBST.
(LIBGUILE_INTERFACE_AGE): new AC_SUBST.
(LIBGUILE_INTERFACE): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_4_INTERFACE_CURRENT): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_4_INTERFACE_REVISION): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_4_INTERFACE_AGE): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_4_INTERFACE): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_13_14_INTERFACE_CURRENT): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_13_14_INTERFACE_REVISION): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_13_14_INTERFACE_AGE): new AC_SUBST.
(LIBGUILE_SRFI_SRFI_13_14_INTERFACE): new AC_SUBST.