Move package to Trash if removal is rejected by OS

Fixes #1418

This commit sends removed packages to "Trash", if their file is still locked
by Windows OS. That's most likely caused by external processes interacting with
that file, which may be anti-virus programs or Sublime Merge holding a lock due
to using the package. Renaming triggers unloading and thus frees the lock.
Trash is cleared at next ST startup.

That's basically the same strategy used to remove libraries.

package_control/package_manager.py

@@ -81,6 +81,7 @@ def __init__(self):
 
         self._available_packages = None
         self._available_libraries = None
+        self.session_time = datetime.datetime.now()
 
         self.settings = {}
         settings = sublime.load_settings(pc_settings_filename())
@@ -1987,16 +1988,30 @@ def delete_package(self, package_name):
         if can_delete_file:
             try:
                 os.remove(package_file)
-            except (OSError, IOError) as e:
-                if self.settings.get('debug'):
-                    console_write(
-                        '''
-                        Unable to remove package "%s" -
-                        deferring until next start: %s
-                        ''',
-                        (package_name, e)
+            except OSError:
+                try:
+                    trash_path = sys_path.trash_path()
+                    os.makedirs(trash_path, exist_ok=True)
+                    # Try to move file to "Trash" directory.
+                    # Required for e.g. Sublime Merge to unload the package and unlock the file.
+                    # Note: Locked files on Windows OS can still be renamed.
+                    trash_path = os.path.join(
+                        trash_path,
+                        hashlib.sha1(
+                            (str(self.session_time) + package_file).encode('utf-8')
+                        ).hexdigest().lower()
                     )
-                result = None
+                    os.rename(package_file, trash_path)
+                except OSError as e:
+                    if self.settings.get('debug'):
+                        console_write(
+                            '''
+                            Unable to remove package "%s" -
+                            deferring until next start: %s
+                            ''',
+                            (package_name, e)
+                        )
+                    result = None
 
         if can_delete_dir:
             if not self.backup_package_dir(package_name):
@@ -2041,7 +2056,7 @@ def backup_package_dir(self, package_name):
             return True
 
         backup_dir = os.path.join(
-            sys_path.data_path(), 'Backup', datetime.datetime.now().strftime('%Y%m%d%H%M%S')
+            sys_path.data_path(), 'Backup', self.session_time.strftime('%Y%m%d%H%M%S')
         )
         package_backup_dir = os.path.join(backup_dir, package_name)