frameencoder: do not allocate noise reduction struct unless NR is enabled

This fixes output mismatch between asm / no-asm for 4:4:4 encodes.  Why? I am
not entirely sure yet, but this is an obvious bug fix.

--HG--
branch : stable
extra : rebase_source : 9a3ffc24b47c1c4b1532f26168c14ba7e9cab5ed
search: do not skip intra tu 32x32 unless TU intra depth is deep (refs #71)

This may not be the best workaround for the bug, and needs a proper long term
fix.

--HG--
branch : stable
encoder: do not allow scaling lists to be used with 4:4:4 color space (refs #72)

It causes hash mistakes

--HG--
branch : stable
extra : amend_source : 4f5a265489b9f66bfb28ecea6f9567167e34d7bd