setup: detect statfs statfs is not defined by POSIX but is available in various systems to help decide filesystem type. Let's detect it and set the macro HAVE_STATFS.

setup: add a function to test header files

setup: split "hasfunction" to test arbitrary code The next patch wants to test include files.

rebase: add flag to require destination In some mercurial workflows, the default destination for rebase does not always work well and can lead to confusing behavior. With this flag enabled, every rebase command will require passing an explicit destination, eliminating this confusion.

update: add flag to require update destination In some mercurial workflows, the default destination for update does not always work well and can lead to confusing behavior. With this flag enabled, every update command will require passing an explicit destination, eliminating this confusion.

mq: reject new patch name containing leading/trailing whitespace We could create a patch of such name, but it wouldn't be processed properly by mq as parseseries() strips leading/trailing whitespace. The test of default message (added by b9a16ed5acec) is no longer be useful so removed. This issue was reported as: https://bitbucket.org/tortoisehg/thg/issues/4693/