shell: provide .gitignore

Here's a .gitignore file for the convenience of casual git users.

- M.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

.gitignore

+# .gitignore for dash
+
+# generated by autogen.sh
+Makefile.in
+/aclocal.m4
+/autom4te.cache/
+/compile
+/config.h.in
+/configure
+/depcomp
+/install-sh
+/missing
+
+# generated by configure
+Makefile
+/config.cache
+/config.h
+/config.log
+/config.status
+/src/.deps/
+/stamp-h1
+
+# generated by make
+/src/token_vars.h
+
+# Apple debug symbol bundles
+*.dSYM/
+
+# backups and patch artefacts
+*~
+*.bak
+*.orig
+*.rej
+
+# OS generated files
+.DS_Store
+.DS_Store?
+._*
+.Spotlight*
+.Trash*
+*[Tt]humbs.db