Add central notification dispatcher for the "general" set of gconf keys.

[David Hampton]

Log Message:
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Add central notification dispatcher for the "general" set of gconf
keys.  This is needed because lots of file need callbacks for just one
or two keys from this section.  Add routines to get/set float values
in gconf.  Miscellaneous tweaks.

Tags:
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gnucash-gnome2-dev

Modified Files:
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    gnucash/src/core-utils:
        gnc-gconf-utils.c
        gnc-gconf-utils.h