properly document panics in div_euclid and rem_euclid

src/libcore/num/mod.rs

@@ -1864,7 +1864,7 @@ if `self < 0`, this is equal to round towards +/- infinity.
 
 # Panics
 
-This function will panic if `rhs` is 0.
+This function will panic if `rhs` is 0 or the division results in overflow.
 
 # Examples
 
@@ -1903,7 +1903,7 @@ This is done as if by the Euclidean division algorithm -- given
 
 # Panics
 
-This function will panic if `rhs` is 0.
+This function will panic if `rhs` is 0 or the division results in overflow.
 
 # Examples
 
@@ -3694,6 +3694,10 @@ Since, for the positive integers, all common
 definitions of division are equal, this
 is exactly equal to `self / rhs`.
 
+# Panics
+
+This function will panic if `rhs` is 0.
+
 # Examples
 
 Basic usage:
@@ -3719,6 +3723,10 @@ Since, for the positive integers, all common
 definitions of division are equal, this
 is exactly equal to `self % rhs`.
 
+# Panics
+
+This function will panic if `rhs` is 0.
+
 # Examples
 
 Basic usage: