Add some common files to .gitignore

Add some OS specific files and Eclipse project files, as well as the
top level build directory because it is recommended in the wiki to
perform your build inside of it.  Also ignore the autom4te.cache
directory.

[tlyu@mit.edu: minor commit message edits]

.gitignore

@@ -15,6 +15,31 @@ obj/
 testdir/
 testlog
 
+# OSX files
+.DS_Store
+
+# Generated by Dolphin for individual settings for directories
+.directory
+
+# Files generated by merges
+*.orig
+
+# Windows thumbnail db
+Thumbs.db
+
+# Eclipse specific files
+.project
+.cproject
+.settings/
+.pydevproject
+.autotools
+
+# Ignore the build directory
+/build/
+
+# The autom4te cache directory
+autom4te.cache/
+
 /doc/version.py
 
 /doc/html/