clang build warnings: 'register' storage class specifier is deprecated

[historic_bruno]

Building on OS X Yosemite, Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)

../../../source/third_party/mongoose/mongoose.cpp:1858:3: warning: 'register'
      storage class specifier is deprecated [-Wdeprecated-register]
  register uint32_t a, b, c, d;
  ^~~~~~~~~

../../../source/collada/Decompose.cpp:127:5: warning: 'register' storage class
      specifier is deprecated [-Wdeprecated-register]
    register double tr, s;
    ^~~~~~~~~

[ben]

In 16708:

Removes use of 'register' storage class, deprecated in C++11. Fixes -Wdeprecated-register build warnings in clang, fixes #3068.

[historic_bruno]

In 22503:

Removes deprecated 'register' storage class from mongoose. Refs #3068