Merge branch 'bp/fsmonitor'

We learned to talk to watchman to speed up "git status" and other
operations that need to see which paths have been modified.

* bp/fsmonitor:
  fsmonitor: preserve utf8 filenames in fsmonitor-watchman log
  fsmonitor: read entirety of watchman output
  fsmonitor: MINGW support for watchman integration
  fsmonitor: add a performance test
  fsmonitor: add a sample integration script for Watchman
  fsmonitor: add test cases for fsmonitor extension
  split-index: disable the fsmonitor extension when running the split index test
  fsmonitor: add a test tool to dump the index extension
  update-index: add fsmonitor support to update-index
  ls-files: Add support in ls-files to display the fsmonitor valid bit
  fsmonitor: add documentation for the fsmonitor extension.
  fsmonitor: teach git to optionally utilize a file system monitor to speed up detecting new or changed files.
  update-index: add a new --force-write-index option
  preload-index: add override to enable testing preload-index
  bswap: add 64 bit endianness helper get_be64

Documentation/technical/index-format.txt

@@ -295,3 +295,22 @@ The remaining data of each directory block is grouped by type:
     in the previous ewah bitmap.
 
   - One NUL.
+
+== File System Monitor cache
+
+  The file system monitor cache tracks files for which the core.fsmonitor
+  hook has told us about changes.  The signature for this extension is
+  { 'F', 'S', 'M', 'N' }.
+
+  The extension starts with
+
+  - 32-bit version number: the current supported version is 1.
+
+  - 64-bit time: the extension data reflects all changes through the given
+	time which is stored as the nanoseconds elapsed since midnight,
+	January 1, 1970.
+
+  - 32-bit bitmap size: the size of the CE_FSMONITOR_VALID bitmap.
+
+  - An ewah bitmap, the n-th bit indicates whether the n-th index entry
+    is not CE_FSMONITOR_VALID.