[CM] autoload compiling when shared libs are in *load-path*

[bil at ccrma.Stanford.EDU]

repl.scm adds "libm.scm" as the autoload info for *libm*.
This could instead be a function that looks for libm_s7.so
in the load-path, checks its write date against the
libm_s7.c in that directory, and loads it if up-to-date.
If none found, it loads "libm.scm".  I'd call it a
"lack of enhancement" not a "bug" (this joke goes all
the way back to Apple in the late '70's when yours
truly was at Apple, typing on an Apple II in a temporary shed
on a parking lot in Cupertino.  The inventory program
I was associated with took more than a month to finish
its monthly report).