30/1/2004: In R-1.8.1, 'object.size' gives an error on certain types of object (e.g. 'externalptr'). Code of 'print.if.small' adjusted to cope.

3/2/2004: getOption( "debug.command.recall") now defaults to FALSE if 'savehistory' would give an error (as it will under ESS, for example), or TRUE otherwise; used to default to TRUE always.

4/2/2004: minor changes to documentation in 'README.debug', mainly to do with ESS.

16/2/2005: added support for 'local.on.exit' to match 'mvbutils'

  Fixed obscure bug to do with missing-mode objects in 'move.to.next.expr'
  
  Fixed buggy display of long subscript-replacement expressions
  
  Fixed bugs with 'skip'ping into exit code
  
  NAMESPACEd it-- with difficulty, owing to the unusual nature of 'debug'.
  
2/4/2005: added 'debug.catfile' option to (by default) print to stderr() rather than stdout(); helps if 'sink' is in operation

20/10/2008: added ESCAPE handling-- drops you back to the debugger prompt, rather than straight back to the terminal. (Unless the interrupt happens while you're in debug's own code-- need some muffleWarnings stuff.)

28/10/2009: for-loop over factors now coerces to character; bug in replacement 'parent.frame' fixed; all references to 'delay' finally expunged (they were there only to help "legal" missing values).

1/3/2010: 'with' statements now debugged, in separate "function" window. Only triggered if in step mode, and only for 'with.default' method. Should extend to 'within', and maybe use similar mechanism for 'try'/'tryCatch'

5/4/2010: bugs fixed with 'Recall' and 'match.call'

6/4/2010: 'with'-style step-into added for 'eval', 'evalq', 'try'. 'step.into.funs' added to control this behaviour.

7/4/2010: bug fixed with changed behaviour of for- and while- loops in R 2.10; these now return NULL.

7/5/2010: bugs fixed for single-statement 'with', for 'enclos' argument in 'eval'/'evalq'/'with', and for launching multiple windows at once (when a parent's window wasn't launched until a child ran). 
 - Added support for 'within'. 
 - All methods of 'with' and 'within' in base-R are now handled seamlessly.
 - Note sneaky trick to trigger go-mode automatically; just put go() inside a breakpoint.
 
20/7/2010: experimental support for time limit on autoprint, via 'debug.print.time.limit' in 'options()' 
 
27/7/2010: bug fix
 - couldn't qqq() when mtracee was called by 'try'-- now uses a new error class that 'try' shouldn't catch

1/12/2011: "<missing>" only printed if in step mode. "<invisible>" printed for invisible! 'suppressWarnings' now handled as per 'eval' etc.

23/4/2012: finally added easy in-package debugging, via eg 'mtrace(mypack:::myfun)'; also for functions that are in a list or environment, via 'mtrace(mything$myfun)'.

7/9/2012: now handles 'eval.parent' properly.
