bug#15413: 24.3.50; Emacs gets hung by find-file for //<TAB>

[Katsumi Yamaoka]

When performing find-file, Emacs gets hung if I mistyped as:

Find file: // and <TAB>

As it might be because C-g doesn't break an inf-loop on Cygwin
Emacs (bug#14553), there seems to be no way to get out of it
except for killing the Emacs process.  For a wonder, Emacs does
not eat CPU so much at that time.

In GNU Emacs 24.3.50.1 (i686-pc-cygwin, GTK+ Version 3.8.2)
 of 2013-09-19 on localhost
Bzr revision: 114379 acm@muc.de-20130918204737-2ed6jt7qnku9okim
Windowing system distributor `The Cygwin/X Project', version 11.0.11403000
Configured using:
 `configure --verbose --with-x-toolkit=gtk3
 --without-dbus --without-gconf --without-gsettings'