use consistent style for all liboctave and libinterp include guards * mex.h, mexproto.h, mxarray.in.h, oct-obj.h, octave-default-image.h: Use include guard style that is consistent with other files in Octave.

header = '{date|shortdate}  {author|person}  <{author|email}>\n\n'
changeset = '\t{desc|tabindent|strip}\n\n\tFiles: {files|stringify|fill68|tabindent|strip}\n\n'