Constraint-facet-pack tests failing due to copy-vs-move issues

[eyalroz]

In tests/facet_pack.cpp we have the test_constrained_fpe() function. It uses move and copy construction counting to check whether certain values are copied or moved - and we fail because there as some copies when there should be moves:

/home/eyalroz/src/mine/strf/test/facets_pack.cpp:384:  test (1 == 0) failed. 
    In function 'void test_constrained_fpe()'
/home/eyalroz/src/mine/strf/test/facets_pack.cpp:387:  test (2 == 0) failed. 
    In function 'void test_constrained_fpe()'
/home/eyalroz/src/mine/strf/test/facets_pack.cpp:390:  test (3 == 0) failed. 
    In function 'void test_constrained_fpe()'
/home/eyalroz/src/mine/strf/test/facets_pack.cpp:393:  test (4 == 0) failed. 
    In function 'void test_constrained_fpe()'
/home/eyalroz/src/mine/strf/test/facets_pack.cpp:396:  test (5 == 0) failed. 
    In function 'void test_constrained_fpe()'

there are additional failures which may or may not be related to these.

The problem seems to be that a lot of move ctors for facet packs, which inherit from fact_pack_base - don't use std::move() when constructing their base class. Which apparently we need to do.

[eyalroz]

Also, there are two redundant ctor's which wouldn't compile if they ever got instantiated...