Trap TERM signal. Without this, bash still executes the EXIT handler upon receiving TERM, but dash doesn't.
Fixes to croutonclip:
 - Proper traps
 - Limit usage of temporary files
 - Detect aura window id.
 - Put VERBOSE tests in if blocks.
Minor fixes to croutonurlhandler.
Major simplification of the logic in croutonxinitrc-wrapper.
Simpler croutonclip detection in xinit.
Improvements to Chromium extension.
Fixes in websocket.c:
 - Split socket_server_accept in 2 chunks.
 - Improved popen2, uses poll/waitpid to check if there is more data
   to read, and if the child process exited.
 - Clean up error messages.
 - Improve comments and formatting.
 - Verify the validity of base64 output.
Pull in xclip package dependency in extension, improve comments.
Rename cros-extension to extension.