Throw if asLong() gets a partially-numeric string

Author: mrkline

docopt_value.h

@@ -259,10 +259,14 @@ namespace docopt {
 	{
 		// Attempt to convert a string to a long
 		if (kind == Kind::String) {
-			// Doesn't guard against trailing characters,
-			// but doing so (if desired) would be trivial by checking pos.
+			const std::string& str = variant.strValue;
 			std::size_t pos;
-			return stol(variant.strValue, &pos); // Throws if it can't convert
+			const long ret = stol(str, &pos); // Throws if it can't convert
+			if (pos != str.length()) {
+				// The string ended in non-digits.
+				throw std::runtime_error( str + " contains non-numeric characters.");
+			}
+			return ret;
 		}
 		throwIfNotKind(Kind::Long);
 		return variant.longValue;