shapefile driver: an integer field is reported as real

[ari.jolma@…]

In ogrshapelayer.cpp:600 the default width for an integer field is set to 11.
This happens, e.g. when you create a new Integer FieldDefn in scripting language.

When you open thus created shapefile, dbfopen.c:1003 reports that it is a Double
(FieldSize > 10).

It seems that the field is actually an integer field but looking at it from
script, it is reported as Real.

[carlh@…]

My guess is that the test at dbfopen.c:1003 is based on the fact that the
largest signed, 32-bit integer value requires 10 characters ("2147483647"). 
However, due to its leading minus sign, the smallest signed, 32-bit integer
value requires 11 characters ("-2147483648").

[warmerdam]

I'm making #3615 the official ticket to address wide integer fields in dbf.