Added --tmpdir option to set the temporary directory

With either --tmpdir or EASYBUILD_TMPDIR you can set the directory used
for temporary storage.
Check if temp storage allows to execute files

If your temp storage is mounted with 'noexec', this can cause problems
for certain easybuilds (numpy). We now print a warning about this.
use -fopenmp instead of -openmp for Intel compilers, Intel's mpif90 only reacts to -fopenmp (+ style fixes)
revert change to generaloption, should be done in vsc-base/separate branch
revert back to using -openmp for enabling OpenMP with Intel compilers
minor style fixes
add -mt_mpi to compiler flags when both usempi and openmp toolchain options are enabled
add test case for ictce toolchain, check whether -mt_mpi is used with usempi/openmp toolchain options enabled
improve error message in case Intel FFTW libraries are not found
add mt_mpi without preceding '-' to list of flags
add support for computing and verifying file checksums (supported: adler32, crc32, md5, sha1)
add 'checksums' easyconfig parameter
log MD5 checksum for source and patch files, verify checksum for source and patch files if it's provided
add unit tests for checksum functionality
fix remarks
update vsc-base with support for --confighelp and (unused) bash tab completion support
add support for using 'size' as checksum, add support for specifying multiple checksums per file
Merge pull request #775 from boegel/vsc-base-update

update vsc-base with support for --confighelp and (unused) bash tab completion support
make sure OAuth token can be supplied for tests that talk to GitHub, to avoid strict API rate limits
Merge pull request #774 from boegel/checksums

add support for computing and verifying source/patch file checksums