streamline .gitignore further

adding some comments, regrouping files and use some patterns to avoid
updating the ignore file for new translations or abi changes

Git-Dch: Ignore

.gitignore

@@ -1,30 +1,36 @@
-aclocal.m4
-autom4te.cache/
-build/
-buildlib/config.guess
-buildlib/config.sub
-configure
-debian/copyright
-doc/de/
-doc/es/
-doc/fr/
-doc/it/
-doc/ja/
-doc/pl/
-doc/pt/
-doc/pt_BR/
-doc/examples/sources.list
-marks.bzr
-marks.git
-debian/*.log
-debian/*.substvars
-debian/*.debhelper
-debian/apt-doc
-debian/apt
-debian/apt-utils
-debian/libapt-pkg4.12
-debian/libapt-inst1.5
-debian/libapt-pkg-dev
-debian/libapt-pkg-doc
-debian/apt-transport-https
-debian/files
+# build artifacts
+/aclocal.m4
+/autom4te.cache/
+/build/
+/buildlib/config.guess
+/buildlib/config.sub
+/configure
+
+# copy of COPYING
+/debian/copyright
+
+# generated files in the process to build all
+# apt man pages and other documentation
+/doc/*/
+!/doc/examples/
+!/doc/po/
+
+# package building artifacts
+/debian/*.log
+/debian/*.substvars
+/debian/*.debhelper
+/debian/files
+/debian/apt/
+/debian/apt-doc/
+/debian/apt-utils/
+/debian/libapt-pkg*/
+/debian/libapt-inst*/
+/debian/libapt-pkg-dev/
+/debian/libapt-pkg-doc/
+/debian/apt-transport-https/
+
+# generated from *.in files
+/doc/examples/sources.list
+/debian/libapt-pkg*.install
+/debian/libapt-inst*.install
+/debian/libapt-pkg-dev.install