Use relative paths in .gitignore to play nice with git submodules.

Closes #25.

Signed-off-by: Benoit Sigoure <tsunanet@gmail.com>

.gitignore

@@ -1,12 +1,23 @@
-/INSTALL
-/Makefile.in
-/aclocal.m4
-/autom4te.cache/
-/build-aux/libtool.m4
-/build-aux/ltoptions.m4
-/build-aux/ltsugar.m4
-/build-aux/ltversion.m4
-/build-aux/lt~obsolete.m4
-/config.h.in
-/configure
-/tests/Makefile.in
+*~
+*.swp
+INSTALL
+Makefile.in
+Makefile
+aclocal.m4
+autom4te.cache/
+build-aux/libtool.m4
+build-aux/ltoptions.m4
+build-aux/ltsugar.m4
+build-aux/ltversion.m4
+build-aux/lt~obsolete.m4
+config.h.in
+configure
+config.h
+config.log
+config.status
+libtool
+stamp-h1
+tests/atconfig
+tests/atlocal
+tests/package.m4
+tests/Makefile.in