transliterate text/use collation before adding to xapian db and when searching

Binary package hint: software-center

As of now software center uses str.lower() when searching in the xapian db:

utils/query.py
22: s = search_term.lower()
33: query = xapian.Query(str_to_prefix[search_prefix]+search_term.lower())

There are two problems with this:
* many languages have diacritic marks for characters but for fast typing users usually write the base character: (in Romanian: ăâșțî and ĂÂȘȚÎ are spelled AASTI by some users).

* characters in the Unicode set can appear in two forms: composed and decomposed: the character U+00C7 (LATIN CAPITAL LETTER C WITH CEDILLA) can also be expressed as the sequence U+0327 (COMBINING CEDILLA) U+0043 (LATIN CAPITAL LETTER C).

To solve both problems both the text entered in the xapian db and the user's text query must be normalized.

The search function in Chromium uses ICU rules to achieve this:
- http://code.google.com/p/chromium/issues/detail?id=1100
- http://www.google.com/codesearch/p?hl=en#OAMlx_jo-ck/src/third_party/WebKit/Source/WebCore/editing/TextIterator.cpp&q=file:TextIterator.cpp&l=1882

There is a python-icu library that could help achieve this. See for example http://lists.osafoundation.org/pipermail/pyicu-dev/2010-October/000214.html

Or one could just remove the diacritical marks from the string altogether: http://stackoverflow.com/questions/517923/what-is-the-best-way-to-remove-accents-in-a-python-unicode-string