osutil: export a "getfstype" method This patch exports the "getfstype" method. So we can use it to enable hardlinks for known safe filesystems. The patch was tested manually via debugshell on a Linux system. "mercurial.osutil.getfstype" works as expected. It's hard to mount filesystem on user-space easily. I will add a test for real hardlink support to indirectly test this patch, after turning on real hardlinks support for certain whitelisted filesystems.

osutil: add a C function getting filesystem type Currently it only has Linux filesystems, according to my Linux manpage, built at 2016-03-15. The code uses "if" instead of "switch" because there could be some duplicated values.

setup: test some header files The next patch will use "statfs", which requires different header files on different platforms. Linux: sys/vfs.h or sys/statfs.h FreeBSD or OSX: sys/param.h and sys/mount.h Therefore test them so we can include the correct ones.

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.