Removed the HttpHeaderEntry constructor that created a "blank" object.

Removed the HttpHeaderEntry constructor that created a "blank" object.
It created problems with the parse() method because id had to be set
to something, but none of the http_hdr_type values were really appropriate,
not to mention they either triggered assertions or confused the statistics.

Now parse() is a static method that calls new HttpHeaderEntry after
parsing has been successful.