Prepare for next release candidate.

Prepare for next release candidate.
* configure.ac, libltdl/configure.ac (AC_INIT): Bump version
number to 2.2.7b.
* libltdl/m4/libtool.m4, libltdl/m4/ltdl.m4,
libltdl/m4/ltoptions.m4, libltdl/m4/lt~obsolete.m4: These files
have been updated without a serial bump since the last release.
* libltdl/Makefile.inc (LTDL_VERSION_INFO): Bump Revision, to
account for bugfixes since the last release.
* libltdl/config/install-sh, libltdl/config/config.guess,
libltdl/config/config.sub, libltdl/config/texinfo.tex,
INSTALL: Updated from canonical source.
* NEWS: Update with missing entries from ChangeLog.
* HACKING: Note workaround for developer tool-path leakage bug.