fix #3106 MSVC handling MSVC_BATCH with targetdir which requires escaping

[bdbaddog]

MSVC handling MSVC_BATCH with targetdir which requires escaping.
If the target dir has a space in it and using batch compiles then the

/Fo argument must end with two dirseps
/Fo".]target dir\\"

Fixes Issue #3106

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated master/src/CHANGES.txt directory (and read the README.txt in that directory)
• I have updated the appropriate documentation

[coveralls]

Coverage increased (+7.6%) to 66.31% when pulling b42fd7c on bdbaddog:msvcbatch_gh_issue_3106 into e7b15e2 on SCons:master.

[coveralls]

Coverage increased (+7.6%) to 66.31% when pulling b42fd7c on bdbaddog:msvcbatch_gh_issue_3106 into e7b15e2 on SCons:master.

[coveralls]

Coverage increased (+7.6%) to 66.31% when pulling b42fd7c on bdbaddog:msvcbatch_gh_issue_3106 into e7b15e2 on SCons:master.