Subs file isn't checked for odd non-ascii characters

[jhill1]

Add the ascii replacer to the import subs file function. Otherwise, you get:

***Error: Failed sbstituting taxa due to unknown error. File a bug report, please!
https://github.com/supertree-toolkit/stk/issues

Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/supertree_toolkit-2.0-py2.7.egg/EGG-INFO/scripts/stk", line 1012, in sub_taxa
XML = supertree_toolkit.substitute_taxa(XML,old_taxa,new_taxa,ignoreWarnings=ignoreWarnings,only_existing=only_existing,generic_match=generic)
File "/usr/local/lib/python2.7/dist-packages/supertree_toolkit-2.0-py2.7.egg/EGG-INFO/scripts/../../stk/supertree_toolkit.py", line 472, in substitute_taxa
XML = stk_phyml.swap_tree_in_XML(XML,new_tree,name)
File "/usr/local/lib/python2.7/dist-packages/supertree_toolkit-2.0-py2.7.egg/EGG-INFO/scripts/../../stk/stk_phyml.py", line 785, in swap_tree_in_XML
t.xpath("tree/tree_string/string_value")[0].text = tree
File "src/lxml/lxml.etree.pyx", line 1031, in lxml.etree._Element.text.set (src/lxml/lxml.etree.c:55347)
File "src/lxml/apihelpers.pxi", line 711, in lxml.etree._setNodeText (src/lxml/lxml.etree.c:24667)
File "src/lxml/apihelpers.pxi", line 699, in lxml.etree._createTextNode (src/lxml/lxml.etree.c:24516)
File "src/lxml/apihelpers.pxi", line 1439, in lxml.etree._utf8 (src/lxml/lxml.etree.c:32441)
ValueError: All strings must be XML compatible: Unicode or ASCII, no NULL bytes or control characters

PS - FIX the typo in the error message

Also, when loading via the GUI, got:
Traceback (most recent call last):
File "/home/jh1889/work/software/supertree-toolkit/autotree/stk_gui/bin/../stk_gui/interface.py", line 2203, in on_import_subs_clicked
dialogs.error_tb(self.main_window,"Error importing sub file:\n"+error)
NameError: global name 'error' is not defined