[ic] backup_database coretag -- some suggested improvements

[Carl Bailey <suppressed>]

We ran into a problem recently doing a multi-table export to an xls 
file from the UI in IC 5.4.  Basically the export looked like it was 
working, but the result was a zero-byte xls file.  Well, after much 
toil and strife, we found out that there is a file-size limit of 
7087104 bytes imposed in the Workbook.pm (part of 
Spreadsheet::WriteExcel).  It's not clear what's behind that 
odd-sounding number, but right there in the module it says, if you need 
bigger spreadsheets, use Spreadsheet::WriteExcel::Big.  That seems to 
be a better default module for Interchange to use.

We made some changes to ~interch/code/UI_Tag/backup_database.coretag

-                require Spreadsheet::WriteExcel;
-                import Spreadsheet::WriteExcel;
+                require Spreadsheet::WriteExcel::Big;
+                import  Spreadsheet::WriteExcel::Big;

-                $xls = 
Spreadsheet::WriteExcel->new("$backup_dir/DBDOWNLOAD.xls");
+                $xls = 
Spreadsheet::WriteExcel::Big->new("$backup_dir/DBDOWNLOAD.xls");

... and this worked very well indeed, since the "Big" module was 
already installed on our server.  No more zero-byte results.

However, we also noticed that the coretag creates XLS files that are 
much larger than necessary for sparsely populated tables (where many of 
the columns are blank, as was true in our case).  So the following 
change (also to backup_database.coretag) made the resulting XLS file 
substantially smaller:

-                $sheet->write_string($i, $j, $fields[$j]);
+                $sheet->write_string($i, $j, $fields[$j]) if 
length($fields[$j]);

This same patch should also work for IC 5.2.  We have not checked 
earlier versions.

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