[mono] safer cleanup

Since we are very close to a release, let's clean up the bigger files.
And later we can cleanup fully.

Merge branch 'xplat-master' into xplat-2017-02

d15.1 Beta preview 2, corresponding to Mono 4.8.0.524

Merge pull request dotnet#1766 from rainersigwald/item-case-sensitivi…

…ty-1751

Item references should be case-insensitive

Work around dotnet#1675 for C++ Code Analysis scenarios (dotnet#1699)

This addresses the repro case for dotnet#1675, but not its root cause. By
providing a `codeBase` for the CA assemblies, we ensure that any running
MSBuild can find them when deserializing a log message.

Merge remote-tracking branch 'origin/vs15-rtw' into xplat-c9

Respect projects that say they only have one TFM (dotnet#1667)

Partially fixes dotnet/sdk#739.

The first iteration of cross-targeting support code unconditionally
queried each ProjectReference for the best TFM to build against, and
then explicitly specified that TFM when building the reference. This
caused a race condition when building a set of projects that had a
single-TFM project and another project that had a reference to it. The
entry point (probably .sln) build would build the referenced project
with no TF specified, and then the referencing project would build it
with an explicit TF specified. These two builds appeared different to
the MSBuild engine (because they had different sets of global
properties) and so were both executed, resulting in a race condition.

The fix is in two parts:
* Allow a project to report back through GetTargetFrameworkProperties
that it only has one TF to build.
* When a project reports that it has only one TF to build, issue its
build request without specifying any TF.

This commit is the latter.

Include implicit imports in GetLogicalProject() (dotnet#1571)

Closes dotnet#1570

[nuget] Fix the nuget-fixup-2.patch file

Added link to up for grabs issues, small formatting changes, cruft re…

…moval