ZipFileRO: Use precise widths for zip file types.

getEntryInfo crashes on 64-bit devices because "long" types
were being passed int pointers (that pointed to a stack frame)
that were reinterpret_cast'ed to long* (sigh.). To fix this issue
once and for all, use types with explicitly defined widths.

This change also removes some dead invariant checking from
Asset.cpp instead of cleaning it up.

Note that we've introduced a wart in NativeLibraryHelper, where
we need to deal with zlib's uLong type, which is "at least 32 bits
wide".

bug: 21622286

Change-Id: Iae675a9601db7aae03a8b80b40321d2cc1d97f50