Runtime test to reproduce threadpool+ProcessExit issue

Do make test-process-exit to run
Fixes threadpool+ProcessExit problem

The threadpool was being shutdown too early, before the ProcessExit event was fired.
This led to bugs such as NLog not shutting down
(http://nlog-project.org/2011/10/30/using-nlog-with-mono.html).
Fix serialization of DateTime struct for MS compatibility

Microsoft uses the UInt64 for the serialized dateData field.
Microsoft also uses Convert.ToUInt64 to convert the serialized
value to UInt64, which results in an overflow exception when
deserializing a DateTime serialized by mono.

Suggested change may break compatibility with previous versions
of mono, but should work with the Microsoft implementation.
Fix for bug 10233 about Socket.BeginSendFile
Subtract sizeof LOSObject instead of LOSObject*

On 64-bit mono with marksweep-conc enabled, sgen_los_pin_object()
would mistakenly set the cardtable_mod_union pointer field to 1
due to the incorrect pointer math in sgen_los_header_for_object()
Client Socket close added
Use standard RFC1123 ("R") format specifier for Expires and Last-Modified headers. Fixes Xamarin bug #10872
Merge pull request #588 from Daniel15/bug-10872

Fix bug #10872 (Expires and Last-Modified headers should use two-digit days)
Merge pull request #585 from mk8/master

Bug 10233 fix proposal for Socket.BeginSendFIle
Prevent path fallback for mono-sgen and pedump

Test updated to allow "mono-sgen" and "pedump" binaries to "walk" the parent
directory to discover the install location of the mono runtime in the same
manner as the "mono" binary.
Merge pull request #589 from qhalid/master

Xamarin Bug 10879: Use of mono-sgen causes mono path detection fallback
Merge pull request #586 from awinters-fvs/awinters/sgen-los-sizeof-fix

[sgen] marksweep-conc 64-bit pointer arithmetic fix for segfault
Misc PCL-related API fixes.
[tests] Test for GC descriptors - first draft.

This runs for a long time and potentially uses lots of memory.  It's not integrated
in the test suite and must be run manually.
[tests] Optional big-switch version of GC descriptor test.

This takes ages to compile with mcs.  See bug #10781.
[tests] Test valuetype GC descriptors, too.
Merge branch 'feature-descriptor-tests'
[sgen] Disable parallel M&S in combination with split nursery.

It crashes at least sgen-weakref-test.exe, and there's more important stuff to
attend to.
Dist the Makefile.am.in files. Fixes #10874.
Runtime assembly mapping for PCL.