Small cleanup to pruneVisit functions

Instead of walking all ASTs and filtering for SymExprs or DefExprs, collect
SymExprs or DefExpers and walk over them directly.  Also replaced some Vecs
with std::vectors.
Merge pull request #33 from daviditen/pruneVisitCleanup

Small cleanup to pruneVisit functions
[Reviewed by hildeth]
various style changes; using atomics instead of reducing arrays
minor style fixes
Merge pull request #34 from benharsh/fannk

Fannkuch cleanup to improve style and use atomics
Merge branch 'master' of github.com:chapel-lang/chapel into aprun-launcher-fix
Make the variables static as they were originally