Bug ID: 2970792 "gradef(s) together with vect package"

I have committed a fix for the bug ID: 2970792 "gradef(s) together with
vect package". With this fix the following parses correctly:

(%i1) prefix("grad");
(%o1)                                grad
(%i2) gradex;
(%o2)                               gradex
(%i3) grad ex;
(%o3)                               grad ex
(%i4) grad(ex);
(%o4)                               grad ex

The bugfix looks for operators, which starts with a literal. For this
case the parser stops parsing the token only, if a whitespace is
following the operator. Therefore, the following shows the old behavior:

(%i5) prefix("<grad");
(%o5)                                <grad
(%i6) <gradex;
(%o6)                              <grad ex

This behavior is necessary to parse operators like "<=" correctly. 

Dieter Kaiser