assignPermeability: Remark on storage order

Clients expect column-major (Fortran) ordering of the contiguous
"permeability_" array so that's what we create despite "tensor"
being row-major.

Suggested by: [at] atgeirr
Add facility for accessing active subset of global data array

This commit introduces a fairly general mechanism for accessing the
active subset of a global grid (property) array.  Essentially, this
takes on the role of translating the active cell index through the
"global_cell" mapping when accessing, e.g., the net-to-gross data
value.

The primary component is class template

    Opm::GridPropertyAccess::Compressed<DataArray,Tag>

which implements a read-only

    value_type operator[](const int c)

that encapsulates and performs the compressed-to-global cell index
translation.  Template parameter "DataArray" is intended as a policy
parameter that for instance wraps access to a "GridProperty<T>" from
module opm-parser (with a fall-back default value if the data is not
specified on input).  The "Tag" parameter is a provision for type
safety--e.g., to prevent passing a region ID into a function that
requires a porosity value.
Reimplement assign* in terms of Compressed<>

This is a demonstration of using the

    GridPropertyAccess::Compressed<>

class template.  We save (some) memory by not creating the zero
fall-back vector in assignPermeability(), preferring instead to use
the fall-back/default mechanism of ArrayPolicy::ExtractFromDeck<>.

While here, adjust vector<PermComponent>::reserve() capacity to
reflect actual requirements.
Fix class reference in documentation

CompressedAccess<> was the former name of class template Compressed<>.
Use correct name in name-space closing comment

Pointed out by [at] atgeirr.
Add missing 'not' in documentation.
Use less restrictive test predicate

This commit replaces uses of BOOST_REQUIRE_* with corresponding
BOOST_CHECK_* facilitites.  This allows greater test coverage if an
individual test fails.

Suggested by: [at] atgeirr
Merge pull request #640 from bska/compressed-array-access

Add Facility for Accessing Active Subset of Global Data Array