Use 7-zip for parallel compression

Since we have a 7-zip dependency, use that to take advantage of multi-core systems to speed up build time a little.
Wintools-builder: co-locate path testing with zip

Put test and zip steps together instead of bulk zip then test
Use 7-zip for parallel compression

Since we have a 7-zip dependency, use that to take advantage of multi-core systems to speed up build time a little.
Merge branch 'master' of https://github.com/pearsonk/openxt
Merge pull request #25 from pearsonk/master

Use 7-zip for parallel compression
Merge pull request #26 from dickon/incremental

improve error handling, logging and incremental behaviour in Windows bui...
Use new build number for the Wix download to fix mkbuildmachine.
Merge pull request #28 from rossphilipson/master

Use new build number for the Wix download to fix mkbuildmachine.
Removed local build instructions that duplicate wiki.

The latest instructions from this file have been moved to the
wiki.
Merge pull request #29 from rossphilipson/master

Removed local build instructions that duplicate wiki.
Missing space in "Program Files (x86)"

Fixed typo for 7-zip envar expansion on 64-bit systems. Lack of curly braces were causing issues in expression (first match to 'programfiles' then handling as text afterward)
Merge pull request #32 from pearsonk/master

Missing space in "Program Files (x86)"