Fix various unsused variable and reordering warnings under Linux
Disable Wmaybe-uninitialized in ply.c
Merge branch 'fix/linux-warnings' into 'master'

Fix a bunch of smaller linux warnings

+1: kelliher, haizhouW, Vien Tran

Merged-on: https://www.assembla.com/code/OpenSurgSim/git/merge_requests/792053