Added wrapper_archiver option

To give user a possibility to choose what archiver he can use another
options was introduced for cd32 and archive wrapper modules. This option
will indicate what archiver should be used for compressing the save
state directories.

fs_uae_wrapper/base.py

@@ -7,6 +7,7 @@ import shutil
 import tempfile
 
 from fs_uae_wrapper import utils
+from fs_uae_wrapper import path
 
 
 class Base(object):
@@ -195,4 +196,15 @@ class Base(object):
             sys.stderr.write("Configuration lacks of required "
                              "`wrapper' option.\n")
             return False
+
+        if 'wrapper_archiver' not in self.all_options:
+            sys.stderr.write("Configuration lacks of required "
+                             "`wrapper_archiver' option.\n")
+            return False
+
+        if not path.which(self.all_options['wrapper_archiver']):
+            sys.stderr.write("Cannot find archiver `%s'." %
+                             self.all_options['wrapper_archiver'])
+            return False
+
         return True