merged branch nikic/doNotUseNameNodeForFuncNames (PR #410)

Commits
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da4d964 Do not use Node_Expression_Name for function names, just use strings for those

Discussion
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Do not use Node_Expression_Name for function names

This patch remove the use of Node_Expression_Name for function names and instead uses normal strings for those. This is mainly to prevent problems with static analysis (e.g. using a loop() function would have triggered with_loop), but it also slightly reduces complexity.