[ccache] PATCH: Clarify docs for sloppiness option include_file_mtime

[Justin Lebar]

Perhaps instead of attaching patches it's easier to send you a pull request?

If so, https://jlebar@github.com/jlebar/ccache.git branch
include-file-mtime-docs.

https://github.com/jlebar/ccache/compare/include-file-mtime-docs

Or alternatively, see below.  :)

diff --git a/MANUAL.txt b/MANUAL.txt
index 4b0cfb2..4be33ae 100644
--- a/MANUAL.txt
+++ b/MANUAL.txt
@@ -420,17 +420,18 @@ WRAPPERS>>.
     ccache can't take for granted. This setting makes it possible to tell
     ccache to relax some checks in order to increase the hit rate. The value
     should be a comma-separated string with options. Available options are:
 +
 --
 *file_macro*::
     Ignore *\_\_FILE__* being present in the source.
 *include_file_mtime*::
-    Don't check the modification time of include files in the direct mode.
+    By default, ccache will not cache a file if it includes a header whose
+    mtime is too new.  This option disables that check.
 *time_macros*::
     Ignore *\_\_DATE\__* and *\_\_TIME__* being present in the source code.
 --
 +
 See the discussion under <<_troubleshooting,TROUBLESHOOTING>> for more
 information.

 *temporary_dir* (*CCACHE_TEMPDIR*)::