* Fix regressions in the `index' builtin. On glibc platforms, this
avoids false positives from a strstr bug in glibc 2.9 through 2.12;
on many other platforms, it fixes two separate regressions, a false
positive introduced in 1.4.11 and a false negative in 1.4.15.
* A number of portability improvements inherited from gnulib.
OBS-URL: https://build.opensuse.org/package/show/Base:System/m4?expand=0&rev=11
