Fix import error if bootstrapping is not yet completed

Fixes #1644

If package_control injector code has not yet been written (first start with
PC4.0 installed), an import error was thown due to missing module.

Regressed by 8e11321

This commit therefore falls back to relative import, in case bootstrapping is
not yet completed.

package_control/package_disabler.py

@@ -5,9 +5,13 @@
 
 import sublime
 
-# Relative import may not work here due to hard loading events
-# into global package_control (see bootstrap.py)!
-from package_control import events
+try:
+    # Relative import does not work here due to hard loading events
+    # into global package_control (see bootstrap.py)!
+    from package_control import events
+except ImportError:
+    # use relative import, if bootstrapping has not yet been completed
+    from . import events
 
 from .console_write import console_write
 from .package_io import package_file_exists, read_package_file