add allBkg option histo needed for fake)
initial import
prefer env python to system one
batch
mkdirIfNeeded
move mkdirIfNeeded from h to cxx

Details:
this fixes the '_POSIX_SOURCE already defined' warning without
polluting all the source code where the header is included. Also, to
be honest I don't quite understand whether this define is really
needed (different explanations on the web).
move implementation to cxx, avoid multiple definition err
fix input filenames, use mkdirIfNeeded
drop single top, now included in ttbar
drop functions using fakePred.file
define initInputFile and call it n times (also does sanity checks)
buildRate: sanity checks and debug printouts
Get: add sanity checks
bail out if cannot build rate
checkPercentages: skip if missing input
checkPercentages: push back default vals to keep vect size in sync
checkPercentages: avoid divide by zero
ugly hack to avoid SR/CR labeling mess. to be removed ASAP.

Details:
I am really confused by the names of the CR/SR, where some of the CR
are labeled as 'SR*', and some of the SR are labeled as 'CR*'. The
bottom line is that here the code is trying to access
'muon_SR_WHSS_all_flavor_den' and the file contains
'muon_CR_WHSS_all_flavor_den'.
Ask Matt about it.
dumpSRTable: skip missing histo
again ugly hack