Merge #1334: fix input range comment for secp256k1_fe_add_int

605e07e fix input range comment for `secp256k1_fe_add_int` (Sebastian Falbesoner)

Pull request description:

  This seems to be a typo that was introduced with commit 4371f98 (PR #1066).

ACKs for top commit:
  sipa:
    ACK 605e07e
  real-or-random:
    ACK 605e07e

Tree-SHA512: 7ee99cf7140c698d1146072734ba986de7328f78b2c076ee445067ef64a6a335c8669f1e733e10f5e14f98b566c799cc4c51b3eb0f036cd178b3c93476c6df2e

src/field.h

@@ -223,7 +223,7 @@ static void secp256k1_fe_negate(secp256k1_fe *r, const secp256k1_fe *a, int m);
 /** Add a small integer to a field element.
  *
  * Performs {r += a}. The magnitude of r increases by 1, and normalized is cleared.
- * a must be in range [0,0xFFFF].
+ * a must be in range [0,0x7FFF].
  */
 static void secp256k1_fe_add_int(secp256k1_fe *r, int a);