dataedit.php and dataedit_exec.php finished

NOTES:
1) These are testing tools. You are free to borrow from their code but
you'll probably have to clean it up a bit -- this was a
several-hour-long hack job.
2) These are not fully tested. If you are editing mission-critical data
make sure the operation worked. Email bugs to me and I'll fix ASAP.
3) The only page you need to manually visit is dataedit.php -- the exec
page is a back-end handler.
4) You can't edit primary keys for a tuple. If we want this feature I'll
add it (shouldn't take long; I left it out because I don't know what
exactly happens when you start changing the pkeys of rows, if anything,
with all our fkey relations.
5) There is no input validation. If you leave fields blank or enter bad
values nothing will yell at you unless the query fails to complete. Be
careful.
header.php modified with $debug = true

I added a $debug variable to the header file that, when true, will
display debugging links on the experimenter header. Since pages have to
be restricted to either participants or experimenters, ONLY
EXPERIMENTERS CAN USE DATAEDIT.PHP for the time being. If this is a
problem we can fix it with a temporary hack.
dataedit_exec bugfix

Typo involving insertion of new experiments resolved.
eExperiments.php basic functionality

Stable, tested version of eExperiments.php ready. Full documentation
pending eSessions.php integration, which is in-progress.

There are some handy functions in here that I might refactor into a
utils.php file. They are:
pgResultsToEditableTableForm($result, $type, $val)
pgResultToTableWithButtons($result, $entryType)

feel free to copy/paste them into your files if they would be useful.
pgResultToTableWithButtons is pretty well written as-is though I'm still
working on the other one.