Add spport for stream parsers to XPath

[ser]

This will enhance the XPath interpreter such that it can operate on streams.

There are, currently, the following stream parsers:

• lightparser
• pullparser
• sax2parser
• streamparser
• ultralightparser

The use case for the PullParser?, StreamParser?, and LightParser? are similar, so only the PullParser? is described.

Sample input

input = "<a><b><c id='1'/><c>x</c></b></a>"

SAX2Parser Use Case

p = SAX2Parser.new(input)
found = false
p.listen( "//c[@id='1']" ) { |uri, local, qname, attrs|
  if attrs['id'] == '1'
    found = true
  else 
    raise "Found wrong c"
  end 
}
raise "c not found" unless found

PullParser?

p = PullParser.new(input)
found = false
for event in p
  if event.matches("//c[text() == 'x']")
    if event[1]['id'].nil?
      found = true
    else
      raise "Found wrong c"
    end
  end
end
raise "c not found" unless found