Documentation/Makefile: fix interrupted builds of user-manual.xml
Unlike gcc, asciidoc does not atomically write its output file or delete it when interrupted. If it is interrupted in the middle of writing an XML file, the result will be truncated input for xsltproc.
XSLTPROC user-manual.html user-manual.xml:998: parser error : Premature end of data in t
Take care of this case by writing to a temporary and renaming it when finished.
Signed-off-by: Jonathan Nieder <firstname.lastname@example.org> Signed-off-by: Junio C Hamano <email@example.com>