Fix OSD_Path::OSD_Path(const TCollection_AsciiString&, const OSD_SysType) on unknown systems
Fix OSD_Path::OSD_Path(const TCollection_AsciiString&, const OSD_SysType) on unknown systems

See https://buildd.debian.org/status/fetch.php?pkg=oce&arch=hurd-i386&ver=0.11-2&stamp=1355676025
several tests fail on Hurd:
    24 - IGESImportTestSuite.testImportIGES_1 (Failed)
    25 - STEPImportTestSuite.testImportAP203_1 (Failed)
    26 - STEPImportTestSuite.testImportAP203_2 (Failed)
    27 - STEPImportTestSuite.testImportAP214_1 (Failed)
    28 - STEPImportTestSuite.testImportAP214_2 (Failed)
    29 - STEPImportTestSuite.testImportAP214_3 (Failed)
    34 - TDataXtdTestSuite.testPattern (Failed)
    35 - UnitsAPITestSuite.testCurrentUnits (Failed)
    36 - UnitsAPITestSuite.testMDTVCurrentUnits (Failed)
because this OSD_Path constructor did nothing when system is unknown.
Use UnixExtract by default.

heartvalve/oce,heartvalve/oce,Tech-XCorp/oce,Tridify/oce,mathstuf/oce,BenoitPerrot/oce,BenoitPerrot/oce,finetjul/oce,finetjul/oce,finetjul/oce,Tridify/oce,finetjul/oce,heartvalve/oce,tpaviot/oce,EvgeneOskin/oce,EvgeneOskin/oce,BenoitPerrot/oce,tpaviot/oce,Tech-XCorp/oce,mathstuf/oce,Tech-XCorp/oce,heartvalve/oce,Tridify/oce,finetjul/oce,BenoitPerrot/oce,mathstuf/oce,EvgeneOskin/oce,EvgeneOskin/oce,Tech-XCorp/oce,mathstuf/oce,Tech-XCorp/oce,Tridify/oce,Tridify/oce,heartvalve/oce,mathstuf/oce,tpaviot/oce,tpaviot/oce,tpaviot/oce,BenoitPerrot/oce,EvgeneOskin/oce