Register new FreeBSD snapshot

Actual file is at https://people.freebsd.org/~asomers/rust/rust-stage0-2016-03-18-235d774-freebsd-x86_64-390b9a9f60f3d0d6a52c04d939a0355f572d03b3.tar.bz2

Author: asomers

src/snapshots.txt

@@ -6,6 +6,7 @@ S 2016-03-18 235d774
   winnt-i386 7703869608cc4192b8f1943e51b19ba1a03c0110
   winnt-x86_64 8512b5ecc0c53a2cd3552e4f5688577de95cd978
   openbsd-x86_64 c5b6feda38138a12cd5c05574b585dadebbb5e87
+  freebsd-x86_64 390b9a9f60f3d0d6a52c04d939a0355f572d03b3
 
 S 2016-02-17 4d3eebf
   linux-i386 5f194aa7628c0703f0fd48adc4ec7f3cc64b98c7