https://bugzilla.gnome.org/show_bug.cgi?id=722254

This method allows removing combining diacritical marks (accents) from strings
used in SPARQL queries. It expects a single argument, the string to be
unaccented.

Note that the output string will also be NFKD-normalized.

Example:

1) First, insert a new element which has accents in the nie:title. In the
example we insert the word 'école' which in UTF-8 NFC looks like
"0xC3 0xA9 0x63 0x6F 0x6C 0x65":

    $ tracker-sparql -u -q "
        INSERT { <abc> a         nie:InformationElement .
                 <abc> nie:title 'école' }"

2) Second, get hexdump of querying nie:title, we should get the original string
in UTF-8 and NFC normalization:

    $ tracker-sparql -q "
        SELECT ?title
        WHERE { <abc> nie:title ?title }" | hexdump
    0000000 6552 7573 746c 3a73 200a c320 63a9 6c6f
    0000010 0a65 000a
    0000013

Or, without the hexdump...

    $ tracker-sparql -q "
        SELECT ?title
        WHERE { <abc> nie:title ?title }"
    Results:
      école

3) Last, apply the unaccenting method. The expected string should look like
"0×65 0×63 0x6F 0x6C 0×65" (i.e. without the combining diacritical mark):

    $ tracker-sparql -q "
        SELECT tracker:unaccent(?title)
        WHERE { <abc> nie:title ?title }" | hexdump
    0000000 6552 7573 746c 3a73 200a 6520 6f63 656c
    0000010 0a0a
    0000012

Or, without the hexdump...

    $ tracker-sparql -q "
        SELECT tracker:unaccent(?title)
        WHERE { <abc> nie:title ?title }"
    Results:
      ecole