[[ Cleanup ]] Fix OS X server build with Xcode 6.1.

Fix incorrect casts that were causing build failures while building
server using clang under Xcode 6.1 on OS X Yosemite.
[[ Bug 13591 ]] Initialise the "shellCommand" on OS X server.

Previously it was only initialised for OS X in desktop mode.
Merge pull request #1557 from peter-b/bugfix-13591

[[ Bug 13591 ]] Initialise the "shellCommand" on OS X server.