maint: Use "fcn" as preferred abbreviation for "function" in libinterp/. * __eigs__.cc, bsxfun.cc, cellfun.cc, daspk.cc, dasrt.cc, dassl.cc, data.cc, debug.cc, error.cc, graphics.cc, graphics.in.h, gzfstream.h, ls-hdf5.cc, lsode.cc, max.cc, oct-opengl.h, quad.cc, strfns.cc, utils.cc, utils.h, variables.cc, __ode15__.cc, gzip.cc, cdef-manager.cc, ov-fcn-handle.cc, ov-java.cc, ov-usr-fcn.cc, bp-table.cc, bp-table.h, lex.h, lex.ll, oct-parse.yy, pt-eval.cc: Replace "func", "fun", "fn" in documentation and variable names with "fcn".

%!function [raa, rbb, igaa, igbb] = sub1 (aa, bb)
%!  global aa bb
%!  aa = 1;
%!  raa = aa;
%!  rbb = bb;
%!  igaa = isglobal ("aa");
%!  igbb = isglobal ("bb");
%!endfunction

%!test <*53579>
%! global aa bb
%! assert (isglobal ("aa"));
%! assert (isglobal ("bb"));
%! aa = 3;
%! xx = 5;
%! [raa, rbb, igaa, igbb] = sub1 (aa, xx);
%! assert (raa, 1);
%! assert (rbb, []);
%! assert (igaa);
%! assert (igbb);
%! assert (xx, 5);
%! clear -global aa bb;  # cleanup after test