PLUGINS: ELF memory manager doesn't work with dynamic detection

[ccawley2011]

The ELF loader provides a memory manager which measures the size of all plugins and uses a heap that's the size of the largest one for loading plugins in order to avoid memory fragmentation. When dynamic detection is enabled, both the detection plugin and an engine plugin are expected to be loaded at the same time, and it's likely that there won't be enough room in the heap for both of them. Defining ELF_NO_MEM_MANAGER at compile time works around this.