Updated Reloading Scheme for ReloadableDLL

[philip-paul-mueller]

Modified the reloading scheme used by ReloadableDLL.
If the library (of the compiled SDFG) is already loaded, through another instance of CompiledSDFG then ReloadableDLL will copy the SDFG library and try to load that until it founds a name that is free.
In ICON4Py we noticed that this leads sometime to a segmentation fault on Linux, but not on MacOS X.
We traced the main issue down to the fact that ReloadableDLL created a copy of the SDFG library without checking if the new name is already used, instead the file is simply overwritten.

The new scheme changes this slightly, in the following ways:

• If the new name is already taken, then no copy is performed and the class tries to use that file, that already exists.
• Instead of copying library n - 1 to n it always makes a copy from the initial library.