var doc: advertise current DEFAULT_PAGER and DEFAULT_EDITOR settings

Document the default pager and editor chosen at compile time in the
git-var(1) manpage so users curious about what command _this_ copy of
git will fall back to when EDITOR, VISUAL, and PAGER are unset can
find the answer quickly.

In builds leaving those settings uncustomized, this patch makes the
manpage continue to say "usually vi" and "usually less" so the
formatted documentation is usable for a wide audience including users
of custom builds that change those settings.  If you would like your
copy of the docs to be less noncommittal, you will need to set
DEFAULT_PAGER=less and DEFAULT_EDITOR=vi explicitly.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -124,6 +124,16 @@ SHELL_PATH ?= $(SHELL)
 # Shell quote;
 SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
 
+ifdef DEFAULT_PAGER
+DEFAULT_PAGER_SQ = $(subst ','\'',$(DEFAULT_PAGER))
+ASCIIDOC_EXTRA += -a 'git-default-pager=$(DEFAULT_PAGER_SQ)'
+endif
+
+ifdef DEFAULT_EDITOR
+DEFAULT_EDITOR_SQ = $(subst ','\'',$(DEFAULT_EDITOR))
+ASCIIDOC_EXTRA += -a 'git-default-editor=$(DEFAULT_EDITOR_SQ)'
+endif
+
 #
 # Please note that there is a minor bug in asciidoc.
 # The version after 6.0.3 _will_ include the patch found here:

Documentation/git-var.txt

@@ -45,13 +45,19 @@ GIT_EDITOR::
     environment variable, then `core.editor` configuration, then
     `$VISUAL`, then `$EDITOR`, and then the default chosen at compile
     time, which is usually 'vi'.
+ifdef::git-default-editor[]
+    The build you are using chose '{git-default-editor}' as the default.
+endif::git-default-editor[]
 
 GIT_PAGER::
     Text viewer for use by git commands (e.g., 'less').  The value
     is meant to be interpreted by the shell.  The order of preference
     is the `$GIT_PAGER` environment variable, then `core.pager`
     configuration, then `$PAGER`, and then the default chosen at
     compile time (usually 'less').
+ifdef::git-default-pager[]
+    The build you are using chose '{git-default-pager}' as the default.
+endif::git-default-pager[]
 
 Diagnostics
 -----------

Makefile

@@ -2191,6 +2191,8 @@ $(XDIFF_LIB): $(XDIFF_OBJS)
 $(VCSSVN_LIB): $(VCSSVN_OBJS)
 	$(QUIET_AR)$(RM) $@ && $(AR) rcs $@ $(VCSSVN_OBJS)
 
+export DEFAULT_EDITOR DEFAULT_PAGER
+
 doc:
 	$(MAKE) -C Documentation all