[GT] Dates in GT

["Weigert, Thomas" <weigert AT mst.edu>]

The recent discussion on dates in GT pointed to one of the hairy
underbellies of GT: the handling of date and time information.

Dates are dealt with in several different ways in GT, which are not
always consistent. The key areas are:

1. Reading of market information
2. Conversion of time frames
3. Selection of time periods in scripts

Some of the issues that are encountered with respect to dates are:

a. some DB reader modules support reading in 3 formats (GT, EU, US),
while others only support one format. In particular, DB::Text was
changed recently to remove support for EU and US format.

b. due to the use of Time::Local in timeframe conversion dates more than
50 years ago (currently before 1959) do not work. So anybody who wants
to use GT for historical analysis is out of luck.

c. due to the use of inconsistent means of recognizing dates on the
command line, users must change the external representation of dates
whenever they operate with different timeframes.

d. almost no error checking is done on dates resulting in cryptic
program aborts when incorrect dates are entered.

I suggest that this is an area where we could help users significantly
if we improved how dates are handled.

Cheers, Th.