Fix potential segfault in ICUs error handling

Summary: `vsnprintf` returns the size of the string regardless of the buffer size.

Fixes #3118

Closes https://github.com/facebook/hhvm/pull/3247

Reviewed By: ptarjan, joelm

Differential Revision: D1447245

Pulled By: svcscm
ReflectionProperty::setValue throws an ReflectionException if unaccessible

Summary: Also changed `gettype() != 'object'` to `!is_object()`

Fixes #3128

Closes https://github.com/facebook/hhvm/pull/3251

Reviewed By: @ptarjan

Differential Revision: D1449439

Pulled By: svcscm