facebook/rocksdb — pull request #268 by huahang (2014-09-04 14:43:35+00:00)
Title: fix a few compile warnings

1, const qualifiers on return types make no sense and will trigger a compile warning: warning: type qualifiers ignored on function return type [-Wignored-qualifiers]

2, class HistogramImpl has virtual functions and thus should have a virtual destructor

3, with some toolchain, the macro __STDC_FORMAT_MACROS is predefined and thus should be checked before define