Use a proper type for the thread indent.

Fixes #172.

Thanks to @vstinner, @jamesjer, and @hroncok for discovering this
problem and suggesting a fix.

Author: 1st1

Diff for: uvloop/includes/stdlib.pxi

@@ -125,7 +125,7 @@ cdef int ssl_SSL_ERROR_WANT_READ = ssl.SSL_ERROR_WANT_READ
 cdef int ssl_SSL_ERROR_WANT_WRITE = ssl.SSL_ERROR_WANT_WRITE
 cdef int ssl_SSL_ERROR_SYSCALL = ssl.SSL_ERROR_SYSCALL
 
-cdef long MAIN_THREAD_ID = <long>threading.main_thread().ident
+cdef uint64_t MAIN_THREAD_ID = <long>threading.main_thread().ident
 
 cdef int subprocess_PIPE = subprocess.PIPE
 cdef int subprocess_STDOUT = subprocess.STDOUT

Diff for: uvloop/loop.pxd

@@ -45,7 +45,7 @@ cdef class Loop:
         bint _running
         bint _stopping
 
-        long _thread_id
+        uint64_t _thread_id
         bint _thread_is_main
 
         object _task_factory

Diff for: uvloop/loop.pyx

@@ -638,7 +638,7 @@ cdef class Loop:
     cdef inline _check_thread(self):
         if self._thread_id == 0:
             return
-        cdef long thread_id = PyThread_get_thread_ident()
+        cdef uint64_t thread_id = PyThread_get_thread_ident()
         if thread_id != self._thread_id:
             raise RuntimeError(
                 "Non-thread-safe operation invoked on an event loop other "