install:module <value>s must be mutually exclusive

...so that only a single one ends up in the .xcd data.  (In the given case,
introduced with 838b77f5f3d6d8fd98891e99a23ff78a6a357cb2 "Resolves: rhbz#1065807
use xdg ~/Templates for default Template location," the duplication for the
unixdesktop case happened to be harmless, as the non-unixdesktop <value>
appeared in a block in main.xcd before the unixdesktop-specific <value>, so the
former was effectively ignored when reading main.xcd.)

Change-Id: I5199556ee3e6decaa07beb14a0503e1b5661f5df
Use cstdlib std::abs instead of stdlib.h abs

...because the latter lacks the abs(long) overload in some popular environments,
cf. <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60401> "stdlib.h does not
provide abs(long) overload."

Similarly, stdlib.h lacks the abs(float), abs(double), abs(long double)
overloads compared to cmath there, whose use was apparently intended in
sw/qa/extras/ooxmlexport/ooxmlsdrexport.cxx.  Rewrote that to use
CPPUNIT_ASSERT_DOUBLES_EQUAL instead, which revealed that the comparisons need
rather large deltas of .1 resp. .2 (which the original code hid with an
implicit conversion to integral type, thus using an effective delta of 1).

Discovered with -Wabsolute-value ("absolute value function 'abs' given an
argument of type 'long' but has parameter of type 'int' which may cause
truncation of value") recently introduced on Clang trunk towards 3.5.

Change-Id: I4c41575ffdccb2944498b662bd3a53fd510cb0c0