[lmi] Double error message

[Greg Chicares]

Kim, I think you had pointed this out. If I remove a required
stylesheet from the data path (deliberately inducing an error),
and then try print preview, I see two separate messageboxes:

Lmi_wx Warning
Error formatting ledger values as xsl-fo: 'Unable to parse xsl stylesheet file 
'/opt/lmi/data/illustration_reg.xsl': Parser failed.
[file C:/lmi/src/lmi/xslt_lmi.cpp, line 93]
'.
[file C:/lmi/src/lmi/ledger_formatter.cpp, line 285]

Error
Unable to read file '/opt/lmi/data/illustration_reg.xsl' required for ledger 
type 'illustration_reg'.
[file C:/lmi/src/lmi/ledger_xsl.cpp, line 67]

where a month ago there was only one IIRC.

Would you rather we work on suppressing the second messagebox
now, or put it off until July because the June release is nigh?
I suggest postponing it, because the obvious fix is not correct
and the correct fix is not altogether simple. Probably it matters
little because users should not be exposed to such errors anyway.