Macro execution of currently recorded macro should be avoided

[westram]

Reproduce (do NOT try on machines with too much memory!):

• run demo.arb
• File/Macros?
• record macro 'infinite.amc'
• click 'Execute' (while still recording)
  ⇒ results in infinite calls of 'infinite.amc', running out of memory/processes
• press 'Stop'
• select 'Expand?', continuing macro recording
• click 'Search' in main window
• press 'Stop' in macro window
• press 'Execute'
  ⇒ results in infinite calls of 'infinite.amc', running out of memory/processes. Once memory is full, macro execution will fail and recursion will terminate (starting to open the 'Search' window). Get some coffee now

Pros: proofs that macro executor behaves as expected while calling hundreds of macros

Solutions:

• ask whether is sure, when 'Execute' is triggered with name of currently recorded macro
  • does not avoid recording two macros which call each other
• add an 'Abort' button to macro window (causing any running macro to terminate)

[westram]

If the macro does some "real work" it will not be possible to

• press the 'Stop' button,
• press ARBs 'Quit' button or
• insert commands in a shell in order to kill arb