darwin: call pthread_setname_np() if available

When setting the process title, also call pthread_setname_np() when
supported (OS X >= 10.6 and iOS >= 3.2.)
build: fix automake serial-tests check again

This effectively undoes the following commits:

    a97685e build: add automake serial-tests version check
    e4c1483 build: serial-tests was added in automake v1.12

After much trial and error I've come to the conclusion that you cannot
reliably test for the automake version inside configure.ac itself.

Feature checks (testing for the presence of macros with m4_ifdef) is
not reliable when the macro is "lazy-loaded" by aclocal: m4 won't see
its definition unless it's actually used in configure.ac, hence checking
for obsolete macros like AM_ENABLE_MULTILIB and AM_WITH_REGEX is not a
reliable proxy for the automake version - both are are lazy-loaded.

That's why this commit moves the version check to autogen.sh, creates
a m4 file with automake options on the fly and includes that in
configure.ac.

Thank you, automake maintainers, for making hard what should be easy.
That's an hour of my life I won't be getting back!
unix: retry waitpid() on EINTR

Before this commit, libuv would abort() if waitpid() failed with EINTR.

It's unlikely that anyone actually hit this error condition: the major
UNIX platforms - with the possible exception of Solaris - don't return
EINTR when the WNOHANG flag is specified, as libuv does.

However, POSIX allows for an implementation to do whatever here: unless
explicitly forbidden, it's allowed and POSIX doesn't restrict
implementers in this particular area.

Let's opt for robustness and handle EINTR.
Merge remote-tracking branch 'origin/v0.10'