build: vcbuild.bat fix for Visual Studio 2012

Change vcbuild.bat to ignore VCINSTALLDIR environment variable,
always check for specific VS version and set GYP_MSVS_VERSION
accordingly. Otherwise GYP generates project files in format
that cannot be compiled by VS2012.
Merge branch 'v0.10'
build: only use DESTDIR instead of PREFIX for pkg

Preserve default install prefix seen in process.config, but use DESTDIR
for installing to deliniate 32/64 versions, avoid conflicts with PREFIX
settings in config.mk
test: reap children when cluster-bind-twice fails