scripts: add guix lint

* guix/scripts/lint.scm: New file. Defines a 'lint' tool for Guix packages.
* tests/lint.scm: New file.
* Makefile.am (MODULES, SCM_TESTS): Add them.
* po/guix/Makevars: Update appropriately.
* po/guix/POTFILES.in: Update appropriately.
* doc/guix.texi: Document "guix lint".

Makefile.am

@@ -89,6 +89,7 @@ MODULES =					\
   guix/scripts/authenticate.scm			\
   guix/scripts/refresh.scm			\
   guix/scripts/system.scm			\
+  guix/scripts/lint.scm				\
   guix.scm					\
   $(GNU_SYSTEM_MODULES)
 
@@ -159,7 +160,8 @@ SCM_TESTS =					\
   tests/nar.scm					\
   tests/union.scm				\
   tests/profiles.scm				\
-  tests/syscalls.scm
+  tests/syscalls.scm				\
+  tests/lint.scm
 
 SH_TESTS =					\
   tests/guix-build.sh				\