Quickcheck against GMP.

This compares pretty much every operation Ramp exposes against the
result of the same computation performed with GMP.

Several bugs/issues were found, and the corresponding tests are
currently commented out: Aatch#24, Aatch#25, Aatch#26, Aatch#27, Aatch#30.

.travis.yml

@@ -17,6 +17,8 @@ script:
   - |
       travis-cargo build -- --features "$FEATURES" &&
       travis-cargo test -- --features "$FEATURES" &&
+      # need optimisations or else a full quickcheck takes too long
+      travis-cargo test --release -- --features "$FEATURES full-quickcheck" &&
       travis-cargo bench -- --features "$FEATURES" &&
       travis-cargo doc -- --features "$FEATURES"
 

Cargo.toml

@@ -19,8 +19,15 @@ path = "src/lib.rs"
 unstable = [] # To keep travis-cargo happy
 asm = []
 
+full-quickcheck = []
+
 [dependencies]
 rand = "0.3"
 
 [build-dependencies]
 gcc = "0.3"
+
+[dev-dependencies]
+rust-gmp = "0.2"
+quickcheck = "0.2"
+quickcheck_macros = "0.2"