This is a feature branch for teaching 'svn patch' to parse
    old mode 100644
    new mode 100755
lines generated by 'git diff'.

Steps:

- [DONE] Implement parse-diff.c support
- [DONE] Implement "make it executable" support, with tests
- [DONE] Implement "make it non-executable" support, with tests
- [DONE] Handle svn:executable and 'new mode' lines both present
- [DONE] parser: Review handling of modes other than 0644/0755
                 Consider checking "mode & 0111"
- [DONE] check rename/copy with mode change; ensure test coverage
- [DONE] ensure binary diff & mode changes interact properly
- [DONE] Teach 'svn diff --git' to emit mode information (executability)
  - In addition to the standard propchange form used for all user properties,
    for compatibility with released 'svn patch' versions
  - Consider the case of an unversioned file being one side of the diff.
  - Use-case?  Who are the current consumers of 'svn diff --git'?

- [TODO] Support symlinks as well (mode 120000)
         - add the 'svn:special' property
         - map the link target representation svn to/from git
  - [DONE] teach parse-diff.c to parse mode 120000
  - [TODO] forbid mode=120000 and svn:special on one file
           (don't know how to parse file contents)
  - [TODO] munge hunks: repository normal form ↔ just the symlink target
  - [TODO] add symlink, remove symlink
  - [TODO] parse mode from "index" lines on file hunks [required for next item]
  - [TODO] change symlink target
  - [TODO] change plain file to symlink
  - [TODO] change symlink to plain file
  - [TODO] teach 'svn diff --git' to emit mode information (symlinks)
  [supporting symlinks is orthogonal to supporting mode changes]