ECPG documentation patch

Hi,

here's the documentation patch for the new ECPG features.

- I changed the order of sections "Using Descriptor Areas" and
  "Informix compatibility mode"
- split the "Using Descriptor Areas", so it now have two subsections:
  "Named SQL Descriptor Areas" and "SQLDA Descriptor Areas".
  The second one talks about the native mode SQLDA only.
- Documented DESCRIBE and the USING/INTO quirks.
- Documented the "string" pseudo-type in compat mode
- Modified the section name "Additional embedded SQL statements",
  it now reads "Additional/missing embedded SQL statements" and
  documented the lack of "FREE cursor_name" statement and
  the behaviour of "FREE statement_name" statement.
- Documented the Informix-compatible SQLDA under the
  "Informix compatibility mode" section.

Best regards,
Zoltán Böszörményi

-- 
Bible has answers for everything. Proof:
"But let your communication be, Yea, yea; Nay, nay: for whatsoever is more
than these cometh of evil." (Matthew 5:37) - basics of digital technology.
"May your kingdom come" - superficial description of plate tectonics

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Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
http://www.postgresql.at/