Problem: Execution stack is incomplete and inefficient.
Solution: Introduce a proper execution stack and use it instead of
sourcing_name/sourcing_lnum. Create a string only when used.
Problem: Cannot map <C-H> when modifyOtherKeys is enabled.
Solution: Add the <C-H> mapping twice, both with modifier and as 0x08. Use
only the first one when modifyOtherKeys has been detected.
Problem: Map functionality mixed with character input.
Solution: Move the map functionality to a separate file. (Yegappan
Lakshmanan, closes#4740) Graduate the +localmap feature.
