Extend SOA handling to support different serial number arrangements

[kdeugau]

(In [773]) /trunk

Start creating SOA serial numbers instead of letting tinydns manage them,
1 of mumble. See #24, sort of.

Tweak the serial on record changes:

• updateSOA()
• addRec()
• updateRec()
• downconvert()
• delRec()

[kdeugau]

(In [774]) /trunk

Add serial numbers on zone creation through API. See #24.

[kdeugau]

(In [775]) /trunk

Add serial numbers on AXFR import. For now we leave non-overwritten SOA
serial entries dangling for overwrite on the next update; this may need
manual intervention later. Most cases should overwrite the SOA for
system/platform consistency. See #24.

[kdeugau]

(In [776]) /trunk

Add retrieval of SOA serial numbers from DB for export. See #24.

First pass adding managed serial number support should be complete. Still
needs some refinements and extending to support schemes other than unixtime.

[kdeugau]

(In [777]) /trunk

Import or generate SOA serial numbers in tiny-import.pl. See #24.

[kdeugau]

(In [781]) /trunk

Move serial number tweaking into a sub for better maintainability. See #24.

[kdeugau]

(In [782]) /trunk

Mispatched change for r781 in delRec(), fixed. See #24.