FileList#<< bypasses exclusions while FileList#include respects them

Problem

The << and include methods behave inconsistently with exclusions:

• exclude then include: exclusion wins (correct)
• exclude then <<: file gets included anyway (bug)

Example

include_list = FileList.new
include_list.exclude 'abc.c'
include_list.include 'abc.c'        # Correctly excluded: []

shovel_list = FileList.new  
shovel_list.exclude 'abc.c'
shovel_list << 'abc.c'              # Bug: returns ["abc.c"]
shovel_list.resolve                 # Still returns ["abc.c"] - resolve doesn't fix it
shovel_list.include 'xyz.rb'        # Now returns ["xyz.rb"], "abc.c" is finally removed

Fix

Add resolve_exclude to the << method:

def <<(obj)
  resolve
  @items << Rake.from_pathname(obj)
  resolve_exclude  # ADD THIS LINE
  self
end

I have a PR with fix & tests ready to go if this approach looks good to maintainers

Start with FileList#<< and compare its exclusion handling with FileList#include and resolve_exclude. Reproduce the abc.c example and verify that a file excluded before being appended remains absent after resolving; confirm the associated fix and tests pass.