Update to 3.1.7. Set LICENSE.

ccache 3.1.7
------------
Release date: 2012-01-08

Bug fixes
~~~~~~~~~

    - Non-writable `CCACHE_DIR` is now handled gracefully when
      `CCACHE_READONLY` is set.
    - Made failure to create files (typically due to bad directory permissions)
      in the cache directory fatal. Previously, such failures were silently and
      erroneously flagged as "compiler produced stdout".
    - Both the `-specs=file` and `--specs=file` forms are now recognized.
    - Added recognition and hashing of GCC plugins specified with
      `-fplugin=file`.
    - `CCACHE_COMPILERCHECK` now also determines how to hash explicit specs
      files (`-specs=file`).
    - Added `CPATH`, `C_INCLUDE_PATH` and similar environment variables to the
      hash to avoid false cache hits when such variables have changed.
    - Corrected log message when unify mode is enabled.
    - Reverted the GCC bug compatibility introduced in ccache 3.1.5 for
      `-MT`/`-MQ` options with concatenated arguments. (The bug is fixed in
      recent GCC versions.)

Other
~~~~~

    - Corrected license header for `mdfour.c`.
    - Improved documentation on how to fix bad object files in the cache.

ccache 3.1.6
------------
Release date: 2011-08-21

New features and improvements
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    - Rewrite argument to `--sysroot` if `CCACHE_BASEDIR` is used.

Bug fixes
~~~~~~~~~

    - Don't crash if `getcwd()` fails.
    - Fixed alignment of ``called for preprocessing'' counter.

ccache 3.1.5
------------
Release date: 2011-05-29

New features and improvements
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    - Added a new statistics counter named ``called for preprocessing''.
    - The original command line is now logged to the file specified with
      `CCACHE_LOGFILE`.
    - Improved error logging when system calls fail.
    - Added support for rewriting absolute paths in `-F`/`-iframework` GCC
      options.
    - Improved order of statistics counters in `ccache -s` output.

Bug fixes
~~~~~~~~~

    - The `-MF`/`-MT`/`-MQ` options with concatenated argument are now handled
      correctly when they are last on the command line.
    - ccache is now bug compatible with GCC for the `-MT`/`-MQ` options with
      concatenated arguments.
    - Fixed a minor memory leak.
    - Systems that lack (and don't need to be linked with) libm are now
      supported.

(wiz)