Partial data recovery (-D flag).

This feature allows to partially recover data from a given segment file
in format suitable for using in COPY FROM statement. List of supported
data types is currently not full and TOAST is not yet supported, but
it's better than nothing. Hopefully data recovery will be improved in
the future.

Implemented by Aleksander Alekseev, reviewed by Dmitry Ivanov, tested
by Dmitry Ivanov and Grigoriy Smolkin.

README.pg_filedump

@@ -59,7 +59,7 @@ not require any manual adjustments of the Makefile.
 ------------------------------------------------------------------------
 Invocation:
 
-pg_filedump [-abcdfhikxy] [-R startblock [endblock]] [-S blocksize] [-s segsize] [-n segnumber] file
+pg_filedump [-abcdfhikxy] [-R startblock [endblock]] [-D attrlist] [-S blocksize] [-s segsize] [-n segnumber] file
 
 Defaults are: relative addressing, range of the entire file, block size
               as listed on block 0 in the file
@@ -71,6 +71,8 @@ The following options are valid for heap and index files:
       off all formatting options)
   -d  Display formatted block content dump (Option will turn off
       all other formatting options)
+  -D  Try to decode tuples using provided list of attribute types.
+      [attrlist] should be something like int,timestamp,bool,uuid
   -f  Display formatted block content dump along with interpretation
   -h  Display this information
   -i  Display interpreted item details