Bug 837267 - [Browser] The URL bar treats any string containing a period as a URL

Port of http://mxr.mozilla.org/mozilla-central/source/docshell/base/nsDefaultURIFixup.cpp#783 used to determine if a string is definitely not a URL

https://bugzilla.mozilla.org/show_bug.cgi?id=837267

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>