find_modules: automatic detection of used modules.

find_modules: automatic detection of used modules.

It's a shell script to parse out used libusual modules
from user source files.  So instead:

  USUAL_DIR =
  USUAL_MODULES =

user can do

  USUAL_DIR =
  USUAL_LOCAL_SRCS =

where USUAL_LOCAL_SRCS contains source files, both .c and .h,
that include libusual files.  Then Setup.mk will launch find_modules
to get actually used list of modules.