Multi-line autocompletion

Allow autocompletion in function calls spanning multiple
lines, e.g.

    install.packages(
        |

should trigger an autocompletion.
Add 'bwdToNearestToken'
Typo
Avoid error on tab insertion when within console
Merge branch 'master' into feature/multiline-autocomplete

Conflicts:
	src/gwt/src/org/rstudio/core/client/Debug.java
	src/gwt/src/org/rstudio/core/client/StringUtil.java
return old tab logic; safer checks for AceEditor grab; escape on first row
Merge branch 'master' into feature/multiline-autocomplete
tidy up a little bit
Use the last index for syntactic quoting
single-line completion when cursor follows '$', '@'
place function argument completions first
Merge pull request #138 from rstudio/feature/multiline-autocomplete

Add support for multi-line autocompletion in R scripts