add constant for shared (GUI/core) setting -dbcache

[Diapolo]

• adds nDefaultDbCache, nMaxDbCache and nMinDbCache in txdb.h

[sipa]

ACK, if pulltester is happy.

[wtogami]

ACK

[laanwj]

ACK

[laanwj]

We could make this nMinDbCache and use it in the GUI as well. AFAIK there is currently no lower bound there.

[Diapolo]

I added nMinDbCache and also use it for the GUI now.

[Diapolo]

@laanwj Have you got a nice and clean idea, how we could share strprintf(_("Set database cache size in megabytes (%d to %d, default: %d)"), nMinDbCache, nMaxDbCache, nDefaultDbCache) with the Qt settings tooltip (which is currently wrong, as I didn't yet update it)?

[laanwj]

@Diapolo IMO the default, min and max do not need to be in the tooltip at all, it should just explain what the setting does. We don't need that in the GUI: the limits are enforced by the widget, and the default is already shown by default :)

[Diapolo]

I removed the tooltip and unneeded defaults from the .ui file but left the min and max in the description, for par we also have such extended infos for example :).

[BitcoinPullTester]

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[jgarzik]

ACK