holiday memleak cleanup part 2

[Lubomir I. Ivanov]

i was seeing a parse-xml.c:entry() memory leak for quite some time
and finally tried to fix it. instead of a single issue there were multiple,
so i've tried resolving all of those in the most harmless way. hopefully
these patches won't break something badly...and if so, at least they
pin-point problematic areas.

mostly related to parsing and merging of components, but there is also a
potential improvement for memory debugging in there.

lubomir
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[PATCH 1/5] Clear memory allocated for event names
[PATCH 2/5] Small changes in the memory management when dive-merging
[PATCH 3/5] Move the memory allocation of entry buffers to a
[PATCH 4/5] When a dive computer is deleted also clear its model
[PATCH 5/5] Clear redundant "description" when merging two cylinder