[INTERNAL] Increase buffer size for LibSSH2SecureFileTransfer

* Profiling on Mac OS X with a 8.9M file showed that a buffer size of
  131072 is about 30% faster than 65536. There was very marginal
  improvement with larger buffers.
[INTERNAL,FIX] When parsing tar header, use left 11 bytes for size

* In the tar specification, the 12th byte of the size field in a
  header can either be a space or NULL (except for >8GB entries). This
  fix makes it correctly handle cases where the byte is a space.
[TEST] Initial stab at tests for TarFile (peakinvestigator)

* Test load with a valid gzip'd tar file containing four spectra, each
  with 14 points.
[BUILD] Add/adjust CMake files to build TarFile_test
[TEST] More extensive testing of TarFile::load()

* Test empty cases and scan mis-match case
[TEST] Simply the TarFile test, and split edge cases for load

* To make test easier to follow, split edge cases for TarFile::load
  into seperate [EXTRA] sections.
* Also create empty and "full" experiments that are duplicated with copy
  constructors as necessary.