improve readability after 7bc5438

Streamline a number of ?: cases and make use of fetchColumn() where it
fits.

* getIPv4AddressNetworkId()
* fetchIPv4AddressNetworkRow()
* getIPv6AddressNetworkId()
* fetchIPv6AddressNetworkRow()
* objectTypeMayHaveParent()
* loadScript()
* getFileCache()
* findFileByName()
* getUserIDByUsername()
* getVLANSwitchInfo()
fix some space-indented lines with tabs
acquireLDAPCache: fix recursive function call
string_insert_hrefs: use preg_replace_callback() instead of preg_replace() with the /e modifier (deprecated, causes a warning with PHP 5.5)
StringInsertHrefsTest: unit test to validate string_insert_hrefs
StringInsertHrefsTest: use a dataProvider for the sample data
don't use argument by reference in doubleLink()

* doubleLink(): update to distinguish input and output data
* getPrevIDforRack(): use function superposition
* getNextIDforRack(): idem
* getProximateRacks(): idem
factor array_fetch() out

There is no core function in PHP that would return a default value when
there is no requested index in the array (consider Array.fetch() in
Ruby). Implement and use such function to replace a few ternary
conditionals with a more focused notation.

* array_fetch(): new function
* syncdomain.php: update
* getPrevIDforRack(): idem
* getNextIDforRack(): idem
* formatRealmName(): idem
* get8021QSyncOptions(): idem
* strerror8021Q(): idem
* renderObject8021QPorts(): idem
* renderObject8021QSyncPorts(): idem
* resolve8021QConflicts(): idem
* tableHandler(): idem
SNMP: list HP J9085A (2610-24)
fix bug I've added in syncdomain.php
commitUpdateAttrValue: don't make dummy SQL UPDATE
refine use of "return" in isInnoDBSupported()
add database triggers to the Link table
renderDepot threw an exception if any objects with an unnamed container existed (#1115)
formatObjectDisplayedName: new function that returns "[ObjectType]" for nameless objects
setDisplayedName: use formatDisplayedName
getContainerInfo: idem
add SNMP support for Cisco WS-C1924 (#1111)
add SNMP support for HP J4900B (#1107)
add SNMP support for AT-GS950/24 (#1105), de-duplicate some code
renderDataIntegrityReport: report on triggers and foreign keys
LinkTriggerTest: remove superfluous globals
LinkTriggerTest: setUp and tearDown the fixture once, instead of before and after each test
StringInsertHrefsTest: setUp and tearDown the fixture once