The MSDEVTOOLS_PATH is the variable defining the location of the various
Microsoft Windows SDK tools used in the JDK windows builds.

In the case of VS2010 + SDK 7 builds it is not being located by default,
forcing the developer to explicitly set ALT_MSDEVTOOLS_PATH to the default VS2010
location which is "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0a" on 64 bit
systems, and the same without " (x86)" on 32 bit systems.
Furthermore the compiler's vcvars[32|64].bat will set "WindowsSdkDir" to point
to that location.
The standalone SDK with VS compilers location is almost the same except
the last component "v7.1"

We should use the value of WindowsSdkDir and the known default locations
to attempt to locate a suitable SDK for use with the VS2010 build.

Having a sanity check that validates the directory is there is also desirable,
and in the event that the user has set ALT_MSDEVTOOLS_PATH it should also check
that there is a "bin" sub-directory.

There is also an inconsistency in that the 32 bit build currently requires
that you set
ALT_MSDEVTOOLS_PATH="C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0a\bin"

 .. note the "\bin" on the end. The 64 bit builds requires that you do not have
this since it appends "bin\x64" for you.

Probably we should make NO bin the rule, since ALT_DEPLOY_MSSDK and ALT_INSTALL_MSSDK
need to point to the same location and do not need "\bin", this making the "\bin" case
the odd one out.