make install: fails if makeinfo unavailable

[mattmill30]

$ make install: fails with "/usr/bin/install: cannot stat './doc/gpm.info'"

When compiling with makeinfo installed, the gpm.texinfo to gpm.info log entry:
if [ "/usr/bin/makeinfo" != "no" ]; then /usr/bin/makeinfo --no-split ./doc/gpm.texinfo -o ./doc/gpm.info; fi

When compiling without makeinfo installed, the gpm.texinfo to gpm.info log entry:
if [ "no" != "no" ]; then no --no-split ./doc/gpm.texinfo -o ./doc/gpm.info; fi

[vapier]

make dist now generates the autotools files. i'd like it to generate the doc files too (like the info page), but the doc subdir Makefile doesn't make this entirely easy. the issue is just that we encode the version in the info page. if we didn't do that, it would be a bit easier ...

[vapier]

hmm, and @release_date@ hasn't existed since commit 95697fb.