When checking the status from waitpid on a kill -STOP <child_pid> WIFSIGNALED returns true

Currently in WIFSIGNALED rust is doing:
(status & 0x7f) + 1
where status is i32

As defined in /usr/include/x86_64-linux-gnu/bits/waitstatus.h
#define __WIFSIGNALED(status) \
  (((signed char) (((status) & 0x7f) + 1) >> 1) > 0)

Here is an example of the issue:
http://paste2.org/fXc8BxJ0

Run it, and it'll print the child pid then:
kill -STOP <child_pid>

Expect:
  Stopped by signal print statement
Results:
  Killed by signal print statement

Using the i32, it wont overflow leaving you with 128 returning true, using the waitstatus define you'll end up with -64 (since it shifts 1 right) which would return false. Though the C version shifts right once not really sure *why* but theres most likely a reason somewhere.

For the fix, just cast to i8 (signed char pretty much) as the C version is doing.

RUNNING ALL TESTS
PASSED 7356 tests

Add clearenv()

Add needed structs for fd passing

Dragonfly fixes 2016-12

This fixes libc again for DragonFly.

Recognize NetBSD/sparc64 as a generic 64-bit NetBSD

The union which contains a void* has to be aligned at a 8-byte boundary.

Keep them in the freebsdlike/mod.rs together with related constants.

Update both mips musl download locations

i686-unknown-openbsd libc correction

Now I had been able to run testsuite on i686-unknown-openbsd, here a batch of corrections.

- `suseconds_t` is `c_long` (`i64` or `i32` depending the arch)
- struct siginfo_t padding adjustment (the pointer `si_addr` makes the pad to change depending pointer size)

I tested the PR on i686-unknown-openbsd and x86_64-unknown-openbsd.

Bump to 0.2.18

Make openbsdlike to support 64 and 32 bits archs

Fix appveyor badge.

Share the host's `target` directory for tests

Move docs back to nightly

This helps caching between runs and can help speed up turnaround time for
various operations. The old android container didn't work out for some reason
due to permissions so the definition has now been vendored locally to just
rebuild it each time.