units: mark _VALGRIND_EXIT as readonly constant

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
units: use dos2unix to split the output of --list-* line by line

Following code didn't work well on windows:

     for f in $(ctags --list-features); do
     	do_something_with $f
     done

This patch introduces dos2unix to split the output of ctags line by line

This is suggested by #116 by @ffes.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
units: allow multiple units

multiple units seprated by comma can be specified with UNITS=.

  $ make -f testing.mak test.units UNITS=bug852368.cpp,bug816636.sml

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
units: simplfy units target