Two problems detected in FdoOwsHttpHandler for x64

[billkellner]

Testing on 64 bits revealed the following two problems:

1. FdoOwsHttpHandler::_headerCallback was incorrectly using the sizeof() a char* rather then the length of the string as an argument to strncmp. This was causing the strncmp to behave incorrectly on 64 bits.

2. FdoOwsHttpHandler::GetLength() was returning 0xffffffff as -1. On 32 bits this was fine, but on 64 bits the value actually returned was 0x00000000ffffffff.