Fix TH1::Clone copy of fFunctions

(cherry picked from commit ba8a1e81e93286adb57ca49abf52bc8387dd96f8)

Conflicts:
	hist/hist/src/TH1.cxx
Quick fix for ROOT-6929.

Proper fix involved implementing Copy for TH2Poly

(cherry picked from commit 71762c5fd26d5890d825e1031537bd63c4ae75ca)