Throw TimeoutCancellationException instead of CancellationException on negative timeout in withTimeout

Fixes #870

Author: qwwdfsad

common/kotlinx-coroutines-core-common/src/Timeout.kt

@@ -25,7 +25,7 @@ import kotlin.jvm.*
  * @param timeMillis timeout time in milliseconds.
  */
 public suspend fun <T> withTimeout(timeMillis: Long, block: suspend CoroutineScope.() -> T): T {
-    if (timeMillis <= 0L) throw CancellationException("Timed out immediately")
+    if (timeMillis <= 0L) throw TimeoutCancellationException("Timed out immediately")
     return suspendCoroutineUninterceptedOrReturn { uCont ->
         setupTimeout(TimeoutCoroutine(timeMillis, uCont), block)
     }

common/kotlinx-coroutines-core-common/test/WithTimeoutTest.kt

@@ -175,7 +175,7 @@ class WithTimeoutTest : TestBase() {
                 expectUnreached()
                 "OK"
             }
-        } catch (e: CancellationException) {
+        } catch (e: TimeoutCancellationException) {
             assertEquals("Timed out immediately", e.message)
             finish(2)
         }