Added helper to open file with emacsclient using filename:line path

Most of console-based utilities prints filename in format
"filename:linenumber". So you may wish to open filename in that format.
This little 'advice' can do that. Just call

emacsclient filename:linenumber

and cursor will be positioned on requested line
Merge pull request #749 from lexa/emacsclient_advice

Added helper to open file with emacsclient using filename:line path
Merge remote-tracking branch 'bbatsov/master' into bbatsov-master