revset: added basic operations to lazyset Added methods __add__, __sub__ and __and__ to duck type more methods in baseset

revset: added lazyset class with basic operations This class allows us to return values from large revsets as soon as they are computed instead of having to wait for the entire revset to be calculated.

tests: test that the pid returned by `hg serve` looks reasonable This failed on windows before win32.spawndetached has been fixed. The process name was "cmd.exe" and not "hg.exe" or "python.exe".

win32: spawndetached returns pid of detached process and not of cmd.exe win32.spawndetached starts the detached process by `cmd.exe` (or COMSPEC). The pid it returned was the one of cmd.exe and not the one of the detached process. When this pid is used to kill the process, the detached process is not killed, but only cmd.exe. With this patch the pid of the detached process is written to the pid file. Killing the process works as expected. The pid is only evaluated on writing the pid file. It is unnecessary to search the pid when it is not needed. And more important, it probably does not yet exist right after the cmd.exe process was started. When the pid is written to the file, waiting for the start of the detached process has already happened. Use this functionality instead of writing a 2nd wait function. Many tests on windows will not fail anymore, all those with the first failing line "abort: child process failed to start". (The processes still hanging around from previous test runs have to be killed first. They still block a tcp port.) A good test for the functionality of this patch is test-treediscovery.t, because it starts and kills `hg serve -d` several times.