Add is_inside_mapping() function to keys.c

Checks whether a mapping handler is currently been executed.
Add unit tests for is_inside_mapping() function
Extract execute_mapping_handler() function in keys

Executes handler for a mapping, if any.
Fix ignoring command-line cmds entered by mapping

Ignore only commands entirely entered by a mapping, not finished
by one.

Thanks to Евгений Жаров (a.k.a. ezharov).

Also see bug ticket #42 at SourceForge.
Merge branch 'fix-ignoring-cmdline-commands-from-mappings'

Fix ignoring command-line commands that entered by a mapping: ignore
only commands entirely entered by a mapping, not finished by one.

Thanks to Евгений Жаров (a.k.a. ezharov).

Also see bug report in ticket #42 at SourceForge.