Unescape properties defined in toolset
Unescape properties defined in toolset

This enables removing the workaround for #704 in the app.config file that
arose because the v14-and-earlier registry-defined toolsets gave unescaped
paths (including the parens in `Program Files (x86)`) but reading them
from an app.config did not.

rainersigwald/msbuild,cdmihai/msbuild,chipitsine/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,sean-gilliam/msbuild,jeffkl/msbuild,mono/msbuild,chipitsine/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,chipitsine/msbuild,mono/msbuild,AndyGerlicher/msbuild,AndyGerlicher/msbuild,Microsoft/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,cdmihai/msbuild,mono/msbuild,rainersigwald/msbuild,Microsoft/msbuild,rainersigwald/msbuild,jeffkl/msbuild,Microsoft/msbuild,jeffkl/msbuild,rainersigwald/msbuild,jeffkl/msbuild,Microsoft/msbuild,cdmihai/msbuild,mono/msbuild,chipitsine/msbuild