[clang-tidy] New: checker misc-unconventional-assign-operator replacing...

[clang-tidy] New: checker misc-unconventional-assign-operator replacing misc-assign-operator-signature

Summary: Finds return statements in assign operator bodies where the return value is different from '*this'. Only assignment operators with correct return value Class& are checked.

Reviewers: aaron.ballman, alexfh, sbenza

Subscribers: o.gyorgy, baloghadamsoftware, LegalizeAdulthood, aaron.ballman, Eugene.Zelenko, xazax.hun, cfe-commits

Differential Revision: http://reviews.llvm.org/D18265

llvm-svn: 268492