shrink-revlog: preserve mode of the shrunken index and data file. Otherwise, the shrunken index file always has mode 0600 thanks to mkstemp(). This is annoying on a server, where multiple users may need to read/write the manifest. chmod()ing the data file is not strictly necessary, but it's nice for consistency.

Fixed a bashism with the use of $RANDOM in hgeditor. The variable $RANDOM is not POSIX so a portable /bin/sh may not define it. When creating a directory with a random name it's better to use mktemp, which, even though is not POSIX, exists in common Unixes including Linux, OpenBSD, FreeBSD and MacOS X.