request for pkglibexecdir

[Eric Blake]

GNU Coding Standards recommend that packages install their subsidiary 
executables in a subdirectory of $(libexecdir), suggesting $(libexecdir)/
$(PACKAGE)[1].  CVS m4 wants to use this idiom for installing its libtool 
modules, rather than $(pkglibdir) which is for object code used in linking 
rather than shared libraries for dlopen'ing.  It would be nice if automake 
provided $(pkglibexecdir) alongside $(pkglibdir) and friends.

[1] http://www.gnu.org/prep/standards/standards.html#Directory-Variables

-- 
Eric Blake