When using File/Save As, File/Import/Import OFX-QFX, File/Import/Import
QIF, or File/Export/Export Accounts, an Open File/Save File dialog is used.

Actual Results:
The default directory in the Open File/Save File dialog is always the
user's home directory.

Requested Result:

For Import/Export: 
1) If the user has never imported/exported a file before, the default
directory should be the user's home directory.
2) If the user has imported/exported a file before, the default directory
should be the last directory used for import/export. There should be unique
default directories for QIF imports, OFX/QFX imports, and Exports in case
the user has these files in different directories. The three unique 'last
directory used' should be saved across sessions.

For File/Save As:
3) If there is no file open in gnucash and if the user hasn't used the
File/Save As in a session, the default directory should be the  directory
of the last file opened in gnucash.
4) If there is a file open in gnucash and if the user hasn't used the
File/Save As in a session, the default directory should be the same as the
directory in which the current open gnucash file resides.
5) If the user has used the File/Save As in a session, the default
directory should be the last directory used for File/Save As. This 'last
directory used' should NOT be saved across sessions. This behaviour would
mimic the File/Open dialog behaviour.