Having this implicit conversion means that we can silently do extra
refcounting when it's completely unnecessary. It's also an obstacle to
making RefPtr more nsRefPtr-like, so let's get rid of it.
The new class is kind of like SystemElf, but using our linker's own symbol
resolution. This also adds some initialization from ELF program headers that
weren't done previously for self_elf, as well as registration as for CustomElf
instances.
In order to avoid adding more dlsym overhead than there already is, resolve
symbols directly in the library containing the linker. (GetSymbolPtr is
essentially free ; dlsym makes the system linker compule a ElfHash itself,
and that's quite expensive to do on all symbols)
This also paves the way for direct symbol resolution in all system libraries.
