Miscellaneous script portability enhancements.

Miscellaneous script portability enhancements.

* aclocal.m4: (GROFF_CSH_HACK): Add space in shebang prototype for
generated conftest.sh script, conforming to portability
recommendation in autoconf docs.
* configure: Likewise, for code generated by GROFF_CSH_HACK.
* contrib/eqn2graph/eqn2graph.sh: Add space in shebang, conforming
to portability recommendation in autoconf docs.
* contrib/gdiffmk/gdiffmk.sh: Likewise.
* contrib/gdiffmk/tests/runtests.in: Likewise.
* contrib/grap2graph/grap2graph.sh: Likewise.
* contrib/groffer/groffer.sh: Likewise.
* contrib/mm/mmroff.pl: Likewise.
* contrib/mom/momdoc/appendices.html: Likewise.
* contrib/pic2graph/pic2graph.sh: Likewise.
* font/devps/generate/afmname: Likewise.
* src/devices/xditview/ad2c: Likewise.
* src/preproc/eqn/neqn.sh: Likewise.
* src/roff/grog/grog.pl: Likewise.
* src/roff/grog/grog.sh: Likewise.
* src/roff/nroff/nroff.sh: Likewise.
* PROBLEMS: Likewise, in embedded script examples.

Improve portability of `pdfroff' shell script.

* arch/misc/shdeps.sh: Add space in shebang, conforming to
portability guidelines in `autoconf' docs.
(PATH_SEARCH_SETUP): New substitution; emits PATH_SEPARATOR
initialization code.  Used by contrib/pdfmark/pdfroff.sh's
`searchpath' function.