[FIX,INTERNAL] Put space between if's and opening parentheses

* To address the Travis CI failure for the cpplint test, put a space
  between if's and opening parentheses
[FIX,INTERNAL] Implement stub method setExpectedHash()

* Log warning when calling setExpectedHash() from
  AbstractSecureFileTransfer and subclasses that do not re-implement
  this function. This provides feedback for incorrect (but non-fatal)
  usage of these classes, and should address a Travis CI strict build
  that flags warnings as errors.
[FIX,INTERNAL] Misc fixes for TarFile (part of PeakInvestigator)

The following changes are all in TarFile::load(), and should address the
warnings-as-errors in the Travis CI build:

* Removed retval as it was unused.
* Change fileSize to an unsigned long long
* Cast the integer num to Size when comparing with size of experiment
[INTERNAL] Remove unused #define BUFFER_SIZE

* After splitting the PeakInvestigator library class into seperate
  classes, the BUFFER_SIZE macro is no longer needed.
[INTERNAL,API] Remove setable buffer size in LibSSH2 class

* The user settable buffer size depended on C99 (?) or later features,
  so a warning was thrown which causes an error in the strict Travis
  build. Removed in favor of a #define macro.