Fix the date time set in file by removing the ':'.

This is the same code than the one under SendCore. The date time should
not have the : (time zone offset) to be able to use the file.
Added test that covers bug 18482.
Fixed bug 18482. Reseting all private key values to null is required because a new import may not overwrite existing values.
Test that DeflateStream.Read does read an empty stream. Covers #19313.
Removed DeflateStream.UnmanagedRead Read loop. Fixes #19313.
If the base_stream was a NetworkStream UnmanagedRead loop would call base_stream.Read a second time and block until one byte was available to return. Without the loop UnmanagedRead will only read the base_stream once.
Fix Mono.Linker.csproj so it can build

Mono.Linker.csproj has drifted from its associated Makefile was was not buildable.
This change applies changes from the last few Makefile changes.
[sgen] Don't crash for describe_ptr() when there's no bridge processor.
Fixed NullReferenceExcepton in Socket.Connect for non-IP endpoints

Socket.Connect(EndPoint) throws a NullReferenceException when connecting to non-IP (eg Unix) endpoints in Dgram mode.
Add a section to CONTRIBUTING.md on inactivity.
[mcs] Recognize await as simple name in type context
[mcs] Fix scope initialization for exception filters using hoisted lambdas with awaited catch clause
[mcs] Fix emit of array access with awaited indexer expression and result field write.
[mcs] Emit side effects of reduced probing expression
[System.Net.Http] Fix disposing of DelegatingHandler. Fixes #20818
[corlib] Fix racy test
Merge pull request #995 from yjoly/master

Fix the date time set in file by removing the ':'.
[sgen] Nicer sgen-grep-binprot output.

Indent events that are always printed so that the ones we're grepping
for are more easily recognized.
[sgen] Binary protocol freeing whole M&S blocks.
[aot] Fix the decoding of MonoJitInfo. Fixes #16439.
[amd64] Fast OP_LREM_IMM for power of two operands.

This was the reason for one of our bad performance results in the
paper "Clash of the Lambdas" by Biboudis, Palladinos, Smaragdakis:

http://cgi.di.uoa.gr/~biboudis/clashofthelambdas.pdf