Merge branch 'jl/submodule-mv'

"git mv A B" when moving a submodule A does "the right thing",
inclusing relocating its working tree and adjusting the paths in
the .gitmodules file.

* jl/submodule-mv: (53 commits)
  rm: delete .gitmodules entry of submodules removed from the work tree
  mv: update the path entry in .gitmodules for moved submodules
  submodule.c: add .gitmodules staging helper functions
  mv: move submodules using a gitfile
  mv: move submodules together with their work trees
  rm: do not set a variable twice without intermediate reading.
  t6131 - skip tests if on case-insensitive file system
  parse_pathspec: accept :(icase)path syntax
  pathspec: support :(glob) syntax
  pathspec: make --literal-pathspecs disable pathspec magic
  pathspec: support :(literal) syntax for noglob pathspec
  kill limit_pathspec_to_literal() as it's only used by parse_pathspec()
  parse_pathspec: preserve prefix length via PATHSPEC_PREFIX_ORIGIN
  parse_pathspec: make sure the prefix part is wildcard-free
  rename field "raw" to "_raw" in struct pathspec
  tree-diff: remove the use of pathspec's raw[] in follow-rename codepath
  remove match_pathspec() in favor of match_pathspec_depth()
  remove init_pathspec() in favor of parse_pathspec()
  remove diff_tree_{setup,release}_paths
  convert common_prefix() to use struct pathspec
  ...

Documentation/technical/api-setup.txt

@@ -8,6 +8,42 @@ Talk about
 * is_inside_git_dir()
 * is_inside_work_tree()
 * setup_work_tree()
-* get_pathspec()
 
 (Dscho)
+
+Pathspec
+--------
+
+See glossary-context.txt for the syntax of pathspec. In memory, a
+pathspec set is represented by "struct pathspec" and is prepared by
+parse_pathspec(). This function takes several arguments:
+
+- magic_mask specifies what features that are NOT supported by the
+  following code. If a user attempts to use such a feature,
+  parse_pathspec() can reject it early.
+
+- flags specifies other things that the caller wants parse_pathspec to
+  perform.
+
+- prefix and args come from cmd_* functions
+
+get_pathspec() is obsolete and should never be used in new code.
+
+parse_pathspec() helps catch unsupported features and reject them
+politely. At a lower level, different pathspec-related functions may
+not support the same set of features. Such pathspec-sensitive
+functions are guarded with GUARD_PATHSPEC(), which will die in an
+unfriendly way when an unsupported feature is requested.
+
+The command designers are supposed to make sure that GUARD_PATHSPEC()
+never dies. They have to make sure all unsupported features are caught
+by parse_pathspec(), not by GUARD_PATHSPEC. grepping GUARD_PATHSPEC()
+should give the designers all pathspec-sensitive codepaths and what
+features they support.
+
+A similar process is applied when a new pathspec magic is added. The
+designer lifts the GUARD_PATHSPEC restriction in the functions that
+support the new magic. At the same time (s)he has to make sure this
+new feature will be caught at parse_pathspec() in commands that cannot
+handle the new magic in some cases. grepping parse_pathspec() should
+help.