Workaround for broken remove() broken

[Niklas Angare <li51ckf02@…>]

operations_test fails on QNX 6.4.0 with:
Warning: line 820 exception reports default_error_condition().value() 1, should be 93

Line 821 also fails with boost::filesystem::remove: Operation not permitted.

The problem is that a workaround for QNX and other OSes in posix_remove() compares the return value of unlink() against EPERM instead of comparing errno against EPERM.

Could it ever have worked? EPERM is typically 1 while the return value from unlink() in case of failure is typically -1.

The attached patch resolves the issue and the operations_test test now passes. As a side note, the test also passes fully with the workaround disabled on QNX 6.4.0.

[Beman Dawes]

(In [50562]) Filesystem: Fix #2531 by applying suggested patch