Crash on saving figure if text.usetex is True

The following test program crashes when matplotlib is built from master on Mac OS X 10.9 (Mountain Lion):

    #!/usr/bin/env python
    import matplotlib
    matplotlib.rc('text', usetex=True)
    from matplotlib import pyplot as plt
    plt.figure()
    plt.plot([0, 1], [0, 1])
    plt.savefig('test.pdf')

The error message looks like this:

	Python(72585,0x7fff72971310) malloc: *** error for object 0x7fa36671ba60: pointer being freed was not allocated
	*** set a breakpoint in malloc_error_break to debug
	Abort trap: 6

`gdb` reveals that the crash occurs in FreeType:

	(gdb) bt
	#0  0x00007fff8383a866 in __pthread_kill ()
	#1  0x00007fff8734235c in pthread_kill ()
	#2  0x00007fff8c206bba in abort ()
	#3  0x00007fff8ca47093 in free ()
	#4  0x00000001038fa296 in destroy_face ()
	#5  0x00000001038fa1d0 in FT_Done_Face ()
	#6  0x000000010388c1ea in std::__1::vector<FT_GlyphRec_*, std::__1::allocator<FT_GlyphRec_*> >::size () at /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/c++/v1/vector:977
	#7  0x000000010388c1ea in FT2Font::~FT2Font (this=0x1097151c0) at src/ft2font.cpp:979
	#8  0x000000010388c16f in FT2Font::~FT2Font (this=0x1097151c0) at src/ft2font.cpp:974
	#9  0x00000001038a4608 in Py::PythonClass<FT2Font>::extension_object_deallocator (_self=0x1097274d0) at ExtensionType.hxx:300
	#10 0x00000001000334b4 in frame_dealloc ()
	#11 0x00000001000a20fc in PyEval_EvalCodeEx ()

And `git bisect` identifies this as a regression in commit f4adec7b569cfd0b30e0f8367ba8618b9e160f92:

    f4adec7b569cfd0b30e0f8367ba8618b9e160f92 is the first bad commit
    commit f4adec7b569cfd0b30e0f8367ba8618b9e160f92
    Author: Michael Droettboom <mdboom@gmail.com>
    Date:   Wed Aug 14 10:18:10 2013 -0400

        Use six instead of 2to3