statfs: change Linux feature detection
Previously we check three things: "statfs" function, "linux/magic.h" and
"sys/vfs.h" headers. But we didn't check "struct statfs" or the "f_type"
field. That means if a system has "statfs" but "struct statfs" is not
defined in the two header files we check, or defined without the "f_type"
field, the compilation will fail.
This patch combines the checks (2 headers + 1 function + 1 field) together
and sets "HAVE_LINUX_STATFS". It makes setup.py faster (less checks), and
more reliable (immutable to the issue above).
Issue351: mq: qrefresh can create extra revlog entry
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ hg qinit
$ echo b > b
$ hg ci -A -m foo
adding b
$ echo cc > b
$ hg qnew -f foo.diff
$ echo b > b
$ hg qrefresh
$ hg debugindex b
rev offset length ..... linkrev nodeid p1 p2 (re)
0 0 3 ..... 0 1e88685f5dde 000000000000 000000000000 (re)