[CMSSW_7_0_X] DMTCP; CGAL; gmp-static; mpfr-static; fix data package permissions

**ChangeLog**
* In CMSSW_7_0_0_pre1 _data-MagneticField-Interpolation_ package had wrong permissions. People outside cms/zh group could not see files. Set all directories on 0755 and all files on 0644.
* In data packages _cURL_ does not download empty files. Touch files before downloading. No issues if wget is used.
* Add _DTMCP_ for SLC5, SLC6 and FC18. Checkpoint/restore implementation.
* Add _gmp-static_ package. GMP static library (w/ PIC) for CGAL (build-time dependency).
* Add _mpfr-static_ package. MPFR static library (w/ PIC) for CGAL (build-time dependency).
* Rename _CGAL_ to _cgal_.
* Second attempt to add_xrootd_ 3.3.3.
* Add `./include/xrootd/private` path to include search path. Needed for CMSSW, but should be removed in future.