Kernel/File: Fixed file read/write hwtests

The 3DS allows the user to read from files opened with the Write access modifier, even if he did not specify the Read access modifier.

Open the files in binary mode so that we can prevent CR/LF problems in Windows, where a line-end is replaced by these two bytes instead of just 0xA, this was causing problems with the GetSize test
Merge pull request #264 from Subv/files

Kernel/File: Fixed file read/write hwtests