Fixed typo Pvdco -> Pvcdo in installed headers
New keywords ENDNUM; IMBNUM and SATNUM.
make sure that the file we are attempting to parse actually exists

before that case was identical to an empty data file...
Merge branch 'new-kw' of https://github.com/osae/opm-parser into polymer_fixes

* 'new-kw' of https://github.com/osae/opm-parser:
  New keywords ENDNUM; IMBNUM and SATNUM.
  Fixed typo Pvdco -> Pvcdo in installed headers