Make collection of expressions per file configurable

[clhunsen]

Right now, during the execution of the 'general' analysis, for each file all #ifdef expressions are collected, but each distinct expression is only collected once per file (comparison via string equality).
see: analyses/general.py, function _wrapFeatureUp()

This should be configurable to affect the construction of these local (per-file) pools.
Like: --localpool [once_per_file | once_per_project | all]

• once_per_file
  • collects each expression once per file
  • per-file-redundant expressions are removed
  • (same behavior as before)
• once_per_project
  • collects each expression once per project
  • all redundant expressions are removed
• all
  • collects all expressions per file
  • no expressions are removed