Add warnings for numeric string keys when reading from intmap

Reviewed By: @paroski

Differential Revision: D1430008
Add warnings for calls to sort on intmaps

Summary: Change dispatch in g_array_funcs of Sort and Usort to WarnAndSort and
WarnAndUsort respectively. This way we don't incur any overhead for regular
kMixedKind arrays.

Reviewed By: @paroski

Differential Revision: D1429736
don't fail test if intl is too old

Summary: This is failing on cmake builds and anoying me in the oncall email

Reviewed By: @JoelMarcey

Differential Revision: D1432980