Add Eclipse metadata directory to ignore list

The Eclipse metadata directory ('.metadata.') may contain some code -
either plugins or history records.

For example, when I searched for "connectUri" in my Java workspace, I
got:

./.metadata/.plugins/org.eclipse.core.resources/.history/57/80e8a247c4fe
00121178f4cf4000aacf
23:	private static final String connectURI 	= "…"

I think that code within the metadata directory should be ignored by
default - the user is probably not searching for plugin code, but for
workspace code.