Don't interpret GB as a timezone name (#129)

Fixes "4 bytes -> GB" being an error saying you can't convert to a
timezone.

This timezone can be obtained in better ways, there's no reason it
should be like this.

core/src/parsing/text_query.rs

@@ -834,7 +834,7 @@ pub fn parse_query(iter: &mut Iter<'_>) -> Query {
                         Conversion::Expr(parse_eq(&mut old))
                     }
                 }
-                Token::Ident(ref s) if Tz::from_str(s).is_ok() => Conversion::Timezone(
+                Token::Ident(ref s) if is_valid_timezone(s) => Conversion::Timezone(
                     Tz::from_str(s).expect("Running from_str a second time failed"),
                 ),
                 _ => Conversion::Expr(parse_eq(iter)),
@@ -845,6 +845,11 @@ pub fn parse_query(iter: &mut Iter<'_>) -> Query {
     }
 }
 
+fn is_valid_timezone(s: &String) -> bool {
+    use std::str::FromStr;
+    s != "GB" && Tz::from_str(s).is_ok()
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

core/tests/query.rs

@@ -549,6 +549,14 @@ fn test_to_timezone() {
     );
 }
 
+#[test]
+fn test_gb_is_gigabytes() {
+    test(
+        "56kbps * 1 year -> GB",
+        "approx. 220.8984 gigabyte (information)",
+    )
+}
+
 #[test]
 fn test_missing_base() {
     test("3 -> base", "Expected decimal base, got eof");