#31 Need to add check for MIT-SHM extension

[Yuri]

I am getting an error:
X Error of failed request: BadImplementation (server does not implement operation)
Major opcode of failed request: 148 (MIT-SHM)
Minor opcode of failed request: 5 (X_ShmCreatePixmap)
Serial number of failed request: 24
Current serial number in output stream: 25

It's better to first check for this extension first, warn the user and to suggest what should be done to fix the problem.

Should be message like this:
Add the line 'Option "MIT-SHM" "Enable"' in "Extensions" section.