Favouring pre-increment according to Cppcheck recommendations.

Cppcheck was run in each subdirectory of VTK and the output of this was run through a Python script that looked for the converting post increment to preincrement warnings and edited the source files appropriately. About 10 files had to be manually changed as the pattern matching failed. The ThirdParty subdirectory was not examined. In total 100 files were changed with 435 insertions/deletions. After these changes, ctest was run and 100% tests passed, 0 tests failed out of 1698.