Use TORSOCKS_* in addition to TSOCKS_*

torsocks used TORSOCKS_* as environment variables since before version
1.0 was even released, according to
https://gitweb.torproject.org/torsocks.git/commit/23818494dcaad8339445f4f6ac948ede5a72b8e4

This commit adds the new variables to ensure backward-compatibility.