merge(3p/git): Merge git subtree at v2.29.2

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

third_party/git/Documentation/Makefile

@@ -17,6 +17,7 @@ MAN1_TXT += git.txt
 MAN1_TXT += gitk.txt
 MAN1_TXT += gitweb.txt
 
+# man5 / man7 guides (note: new guides should also be added to command-list.txt)
 MAN5_TXT += gitattributes.txt
 MAN5_TXT += githooks.txt
 MAN5_TXT += gitignore.txt
@@ -30,6 +31,7 @@ MAN7_TXT += gitcredentials.txt
 MAN7_TXT += gitcvs-migration.txt
 MAN7_TXT += gitdiffcore.txt
 MAN7_TXT += giteveryday.txt
+MAN7_TXT += gitfaq.txt
 MAN7_TXT += gitglossary.txt
 MAN7_TXT += gitnamespaces.txt
 MAN7_TXT += gitremote-helpers.txt
@@ -77,6 +79,7 @@ API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technica
 SP_ARTICLES += $(API_DOCS)
 
 TECH_DOCS += MyFirstContribution
+TECH_DOCS += MyFirstObjectWalk
 TECH_DOCS += SubmittingPatches
 TECH_DOCS += technical/hash-function-transition
 TECH_DOCS += technical/http-protocol
@@ -91,6 +94,7 @@ TECH_DOCS += technical/protocol-capabilities
 TECH_DOCS += technical/protocol-common
 TECH_DOCS += technical/protocol-v2
 TECH_DOCS += technical/racy-git
+TECH_DOCS += technical/reftable
 TECH_DOCS += technical/send-pack-pipeline
 TECH_DOCS += technical/shallow
 TECH_DOCS += technical/signature-format
@@ -123,7 +127,8 @@ ASCIIDOC_HTML = xhtml11
 ASCIIDOC_DOCBOOK = docbook
 ASCIIDOC_CONF = -f asciidoc.conf
 ASCIIDOC_COMMON = $(ASCIIDOC) $(ASCIIDOC_EXTRA) $(ASCIIDOC_CONF) \
-		-agit_version=$(GIT_VERSION)
+		-amanversion=$(GIT_VERSION) \
+		-amanmanual='Git Manual' -amansource='Git'
 TXT_TO_HTML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_HTML)
 TXT_TO_XML = $(ASCIIDOC_COMMON) -b $(ASCIIDOC_DOCBOOK)
 MANPAGE_XSL = manpage-normal.xsl
@@ -147,32 +152,9 @@ endif
 -include ../config.mak.autogen
 -include ../config.mak
 
-#
-# For docbook-xsl ...
-#	-1.68.1,	no extra settings are needed?
-#	1.69.0,		set ASCIIDOC_ROFF?
-#	1.69.1-1.71.0,	set DOCBOOK_SUPPRESS_SP?
-#	1.71.1,		set ASCIIDOC_ROFF?
-#	1.72.0,		set DOCBOOK_XSL_172.
-#	1.73.0-,	no extra settings are needed
-#
-
-ifdef DOCBOOK_XSL_172
-ASCIIDOC_EXTRA += -a git-asciidoc-no-roff
-MANPAGE_XSL = manpage-1.72.xsl
-else
-	ifndef ASCIIDOC_ROFF
-	# docbook-xsl after 1.72 needs the regular XSL, but will not
-	# pass-thru raw roff codes from asciidoc.conf, so turn them off.
-	ASCIIDOC_EXTRA += -a git-asciidoc-no-roff
-	endif
-endif
 ifndef NO_MAN_BOLD_LITERAL
 XMLTO_EXTRA += -m manpage-bold-literal.xsl
 endif
-ifdef DOCBOOK_SUPPRESS_SP
-XMLTO_EXTRA += -m manpage-suppress-sp.xsl
-endif
 
 # Newer DocBook stylesheet emits warning cruft in the output when
 # this is not set, and if set it shows an absolute link.  Older
@@ -197,11 +179,13 @@ ifdef USE_ASCIIDOCTOR
 ASCIIDOC = asciidoctor
 ASCIIDOC_CONF =
 ASCIIDOC_HTML = xhtml5
-ASCIIDOC_DOCBOOK = docbook45
+ASCIIDOC_DOCBOOK = docbook5
 ASCIIDOC_EXTRA += -acompat-mode -atabsize=8
 ASCIIDOC_EXTRA += -I. -rasciidoctor-extensions
 ASCIIDOC_EXTRA += -alitdd='&\#x2d;&\#x2d;'
 DBLATEX_COMMON =
+XMLTO_EXTRA += --skip-validation
+XMLTO_EXTRA += -x manpage.xsl
 endif
 
 SHELL_PATH ?= $(SHELL)
@@ -311,6 +295,7 @@ cmds_txt = cmds-ancillaryinterrogators.txt \
 	cmds-plumbingmanipulators.txt \
 	cmds-synchingrepositories.txt \
 	cmds-synchelpers.txt \
+	cmds-guide.txt \
 	cmds-purehelpers.txt \
 	cmds-foreignscminterface.txt
 
@@ -318,7 +303,7 @@ $(cmds_txt): cmd-list.made
 
 cmd-list.made: cmd-list.perl ../command-list.txt $(MAN1_TXT)
 	$(QUIET_GEN)$(RM) $@ && \
-	$(PERL_PATH) ./cmd-list.perl ../command-list.txt $(QUIET_STDERR) && \
+	$(PERL_PATH) ./cmd-list.perl ../command-list.txt $(cmds_txt) $(QUIET_STDERR) && \
 	date >$@
 
 mergetools_txt = mergetools-diff.txt mergetools-merge.txt