Minor stylistic and code changes for consistency

The most significant changes are:
* Removed underscore prefixes from wbLog??? supporting variables and functions (variables with a leading underscore are reserved as global identifiers by some implementations)
* Renamed variables to be consistent across the wbTime??? structures and functions
* Reflowed wbImport() so that comments are paired with the actions they're describing
* Increased tolerance for floating-point comparisons to three significant digits
Inserted checks for malloc() returning NULL in wbImport()
Replaced the while (...) loop in wbImport() with a for (...) loop that checks for writing past the bounds of the array
Wrapped the global variable gTimerInfoList in namespace wbInternal {}; renamed to timerInfoList
Moved sanity test of wbTimeType to wbClock_start() and wbClock_stop()
Implemented a check for wbTime_start() / wbTime_stop() timer pairing

The list member function std:find() returns wbInternal::timerInfoList.end() if no match is found; therefore, we need to check that the parameters passed in to wbTime_stop() correspond to an actual wbTimerInfo struct inserted by wbTime_start()
Merge remote-tracking branch 'upstream/master'
Updated CMakeLists.txt so that CUDA_HOST_COMPILER is set to /usr/bin/gcc on OS X

This corrects the compiling errors experienced by users of cmake 2.8.10+ on OS X (reported in issue #30)
Type cast the parameter 'level' in wbLog() to type wbLogLevel

This corrects the Visual Studio compiling error noted on the course forum https://class.coursera.org/hetero-2012-001/forum/thread?thread_id=1521&post_id=5702
Qualified parameters that should be invariant with 'const'
Wrapped all remaining 'internal' functions and structures in namespace wbInternal {}
Removed underscore prefix from _wbLog() templates
Merge remote-tracking branch 'upstream/master'