+ fix stack overflow error
+ fix whitespaces
+ fix anti-aliasing issue
+ fix issues with force constraint
+ fix expressions
fixes #1740 quote pov-ray binary on windows

this fixes a bug introduced by 3523741e96d0b8db338f8f05f13282f90ccbbe67
it restores the double quotes for the shell and uses single quotes for the
python string.
fixes #1782 remove unused precsion parameters

from gp_Trsf::SetValues
use Icons for Refine and Increase tolerance features
issue #1027 use unicode filepaths
+ fix build problems with Python & MacOSX
Sketcher: Element Widget enhancement: Support for external geometry

Python naming used is "ExternalEdge" for consistency with the name appearing in the status bar when selecting that object.

As discussed:
http://forum.freecadweb.org/viewtopic.php?f=10&t=6861&sid=bd9ad10357f8a7de146c4fbd2d53c23b&start=90
issue #1573 remove unavailable headers
+ share GL widgets when creating further 3d views of a document
+ fix build failure
issue #1788 SVG output of trimmed curves
fixes #1706 rename anaglyph stereo mode red/cyan
move exportDRAWEXE.py to Sandbox WB
+ fixes #0001779: memory leak
+ fixes #0001735: Ellipsoids visibility problems
Draft: Disabled automatic DXF library download - fixes #1785

Note for existing users: Can be reenabled in menu Edit > Preferences >
Import-Export > DXF > Automatic update