Allow default-value for concrete-inheritance to be instantiable

[nederdirk]

We use concrete-inheritance for our 'setting' table[1], and encountered the buggy situation in which we had application crashes on development environments (lots of branch-switching) where a recently-introduced type present in the database would instantiate a nonexisting class.

This patch defaults the behaviour of SettingQuery()->find() to return the base class for unknown types, instead of Package\\Setting, by using the (correctly-namespaced) classname in TableMap::OM_CLASS.

I added a test that verifies that the base class name is returned from TableMap::getOMClass() with an unexpected value.

[1]: example column.

        <column
            name="type"
            type="ENUM"
            required="true"
            default="string"
            valueSet="'string','int','boolean','datetime','country'"
            inheritance="single"
        >
            <inheritance key="string" class="Setting" />
            <inheritance key="int" class="IntegerSetting" extends="Setting" />
            <inheritance key="boolean" class="BooleanSetting" extends="Setting" />
            <inheritance key="datetime" class="DateTimeSetting" extends="Setting" />
            <inheritance key="country" class="CountrySetting" extends="Setting" /><!-- recently introduced -->
        </column>

[codecov-commenter]

Codecov Report

Merging #1771 (a4933fd) into master (1a3140e) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #1771      +/-   ##
============================================
+ Coverage     87.87%   87.89%   +0.01%     
  Complexity     7826     7826              
============================================
  Files           267      267              
  Lines         22543    22544       +1     
============================================
+ Hits          19810    19815       +5     
+ Misses         2733     2729       -4     

Flag	Coverage Δ
5-max	87.89% <100.00%> (+0.01%)	:arrow_up:
7.4	87.89% <100.00%> (+0.01%)	:arrow_up:
agnostic	73.34% <100.00%> (+<0.01%)	:arrow_up:
mysql	70.19% <100.00%> (+0.31%)	:arrow_up:
pgsql	70.12% <100.00%> (+0.31%)	:arrow_up:
sqlite	68.11% <100.00%> (+0.31%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...rc/Propel/Generator/Builder/Om/TableMapBuilder.php	95.06% <100.00%> (+<0.01%)	:arrow_up:
src/Propel/Runtime/ActiveQuery/Criteria.php	89.97% <0.00%> (+0.44%)	:arrow_up:

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