Log Message:
Update to 1.6.12:

Version 1.6.12rc01 [June 6, 2014]
  Relocated new code from 1.6.11beta06 in png.c to a point after the
    declarations (Max Stepin).

Version 1.6.12rc02 [June 7, 2014]
  Changed file permissions of contrib/tools/intgamma.sh,
    test-driver, and compile from 0644 to 0755 (Cosmin).

Version 1.6.12rc03 [June 8, 2014]
  Ensure "__has_attribute()" macro exists before trying to use it with
    old clang compilers (MacPorts Ticket #43939).

Version 1.6.12 [June 12, 2014]
  No changes.