documentation: Makefile accounts for SHELL_PATH setting

Ensure that the Makefile that generates and installs the Documentation is
aware of any SHELL_PATH setting.  Use this value if found or the current
setting for SHELL if not.  This is an accommodation for systems where sh
is not POSIX enough.

Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/Makefile

@@ -103,6 +103,10 @@ ifdef DOCBOOK_SUPPRESS_SP
 XMLTO_EXTRA += -m manpage-suppress-sp.xsl
 endif
 
+SHELL_PATH ?= $(SHELL)
+# Shell quote;
+SHELL_PATH_SQ = $(subst ','\'',$(SHELL_PATH))
+
 #
 # Please note that there is a minor bug in asciidoc.
 # The version after 6.0.3 _will_ include the patch found here:
@@ -178,7 +182,7 @@ install-pdf: pdf
 	$(INSTALL) -m 644 user-manual.pdf $(DESTDIR)$(pdfdir)
 
 install-html: html
-	sh ./install-webdoc.sh $(DESTDIR)$(htmldir)
+	'$(SHELL_PATH_SQ)' ./install-webdoc.sh $(DESTDIR)$(htmldir)
 
 ../GIT-VERSION-FILE: .FORCE-GIT-VERSION-FILE
 	$(QUIET_SUBDIR0)../ $(QUIET_SUBDIR1) GIT-VERSION-FILE
@@ -240,7 +244,7 @@ user-manual.xml: user-manual.txt user-manual.conf
 
 technical/api-index.txt: technical/api-index-skel.txt \
 	technical/api-index.sh $(patsubst %,%.txt,$(API_DOCS))
-	$(QUIET_GEN)cd technical && sh ./api-index.sh
+	$(QUIET_GEN)cd technical && '$(SHELL_PATH_SQ)' ./api-index.sh
 
 $(patsubst %,%.html,$(API_DOCS) technical/api-index): %.html : %.txt
 	$(QUIET_ASCIIDOC)$(ASCIIDOC) -b xhtml11 -f asciidoc.conf \
@@ -285,7 +289,7 @@ $(patsubst %.txt,%.texi,$(MAN_TXT)): %.texi : %.xml
 
 howto-index.txt: howto-index.sh $(wildcard howto/*.txt)
 	$(QUIET_GEN)$(RM) $@+ $@ && \
-	sh ./howto-index.sh $(wildcard howto/*.txt) >$@+ && \
+	'$(SHELL_PATH_SQ)' ./howto-index.sh $(wildcard howto/*.txt) >$@+ && \
 	mv $@+ $@
 
 $(patsubst %,%.html,$(ARTICLES)) : %.html : %.txt
@@ -299,14 +303,14 @@ $(patsubst %.txt,%.html,$(wildcard howto/*.txt)): %.html : %.txt
 	mv $@+ $@
 
 install-webdoc : html
-	sh ./install-webdoc.sh $(WEBDOC_DEST)
+	'$(SHELL_PATH_SQ)' ./install-webdoc.sh $(WEBDOC_DEST)
 
 quick-install: quick-install-man
 
 quick-install-man:
-	sh ./install-doc-quick.sh $(DOC_REF) $(DESTDIR)$(mandir)
+	'$(SHELL_PATH_SQ)' ./install-doc-quick.sh $(DOC_REF) $(DESTDIR)$(mandir)
 
 quick-install-html:
-	sh ./install-doc-quick.sh $(HTML_REF) $(DESTDIR)$(htmldir)
+	'$(SHELL_PATH_SQ)' ./install-doc-quick.sh $(HTML_REF) $(DESTDIR)$(htmldir)
 
 .PHONY: .FORCE-GIT-VERSION-FILE