Win32: support 64-bit compilation with MSVC. There are lots of C4244 warnings (conversion from 'type1' to 'type2', possible loss of data), so they were disabled. The same applies to C4267 warnings (conversion from 'size_t' to 'type', possible loss of data), most notably - conversion from ngx_str_t.len to ngx_variable_value_t.len (which is unsigned:28). Additionally, there is at least one case when it is not possible to fix the warning properly without introducing win32-specific code: recv() on win32 uses "int len", while POSIX defines "size_t len". The ssize_t type now properly defined for 64-bit compilation with MSVC. Caught by warning C4305 (truncation from '__int64' to 'ssize_t'), on "cutoff = NGX_MAX_SIZE_T_VALUE / 10" in ngx_atosz()). Several C4334 warnings (result of 32-bit shift implicitly converted to 64 bits) were fixed by adding explicit conversions. Several C4214 warnings (nonstandard extension used: bit field types other than int) in ngx_http_script.h fixed by changing bit field types from uintptr_t to unsigned.