writePhase writing binary 0/1 instead of ASCII 0/1

[grady]

At some point between commit 9a1e0fe and c9764e2, there seems to have been a bug introduced to the writePhase code. The phase file output is now writing raw binary 0/1 bytes to the output file, instead of ASCII 0/1 characters.
I.e., the phase lines output have something like (using carat notation)

^@^A^@^@^@^@^A^@.....
^A^@^@^@^@^A^@^@....
....

Instead of

01000010...
10000100...
...