[pfff] rename dots token to ellipsis

Summary:
... this better matches PHP/HHVM token naming. DOTS made
 sense when ellipses could only show up in pfff-only "match variable
 arguments".

Test Plan: make succeeds!

Reviewers: jwatzman, hansonw, pieter

Reviewed By: pieter

Differential Revision: https://phabricator.fb.com/D1648146

Signature: t1:1648146:1414626807:71b2f239e752ec38f5f0c3061e7be5a6d8f262a1
[pfff] fix arg unpacking semantics

Summary:
The unpack operator can be applied to any expression, as long
 as it happens within a function call.

Test Plan: make

Reviewers: hansonw, jwatzman, pieter

Reviewed By: pieter

Differential Revision: https://phabricator.fb.com/D1648160

Signature: t1:1648160:1414626928:15d3b5700daa5621e074fa1579c78258e775f014
[pfff] support for abstract final

Summary:
'abstract final class' is now allowed to support the 'class
 with static utility methods' pattern that's fairly common in PHP
 codebases (especially pre-namespaces ones).

Test Plan: make

Reviewers: jwatzman, pieter

Reviewed By: pieter

Differential Revision: https://phabricator.fb.com/D1648175

Signature: t1:1648175:1414626868:749688fc54f93acb738b2fde0bae2b9d93b14c85