Typo.
SimTK::String::trimWhiteSpace() failed when applied to binary data.

VC++ 2013 std::isspace() (the C-compatible version that takes an int argument) has a bug catcher in Debug mode that objects to being passed an int value that is out of range for an unsigned char. If String::trimWhiteSpace() is called on a binary file, it can blow this check. Casting the char to unsigned char prior to calling isspace() fixes the problem.

I know it sounds absurd to trim white space on a binary file, but it came up while trying to read the contents of an .stl file to determine whether it is in ascii or binary format. It turned out to be binary!
Add STL reader to SimTK::PolygonalMesh class.
Fixes #57.

- Can now read ascii and binary STL mesh files (can force ascii with .stla suffix). Catches and reports most file format problems.
- Supports some STL extensions for Gazebo compatibility (comment lines, "color" keyword ignored).
- Added a new adhoc test LookAtPolygonalMesh that reads mesh files and tries to make contact geometry out of them (very fussy). If it fails it will try to explain why.
- Added PolygonalMesh::loadFile() method that examines the file extension to determine what format to try.
- Added PolygonalMesh::loadObjFile() signature that takes a path name (previousl required an open stream).
- Updated a test case to use the friendlier loadObjFile() method.
Merge pull request #176 from simbody/addSTLreader-issue57

Add STL reader for Simbody's PolygonalMesh class