Make pam_cap compilation conditional.

Default is for make to guess if the user wants the module or not
user can override with

    make PAM_CAP={yes|no}

Thanks to Chris Freidhoff for the suggestion and a first stab at a patch.

Signed-off-by: Andrew G. Morgan <morgan@kernel.org>
diff --git a/Makefile b/Makefile
index 14f0dce..52f7b42 100644
--- a/Makefile
+++ b/Makefile
@@ -10,7 +10,9 @@
 
 all install clean: %: %-here
 	$(MAKE) -C libcap $(MAKE_DEFS) $@
+ifneq ($(PAM_CAP),no)
 	$(MAKE) -C pam_cap $(MAKE_DEFS) $@
+endif
 	$(MAKE) -C progs $(MAKE_DEFS) $@
 	$(MAKE) -C doc $(MAKE_DEFS) $@