bash-completion for make target with colon fails

[Christian Hujer]

Given the following Makefile

```
foo\:bar:
 echo foo >$@
```

When completing
Expected: Then completion completes to "foo:bar"
Actual: Then completion completes to "foo"

Change needed: The completion needs to ignore a colon in the target name when the colon is prefixed with a backslash.

[Christian Hujer (christian.hujer)]

This might be the same bug:
Given the following Makefile
```
foo\ bar:
 touch "$@"
```

When completing
Expected: Then completion completes to "foo\ bar"
Actual: Then completion offers "foo" and "bar" for completion

Change needed: The completion needs to support escapes, ignoring spaces and colons in the target name when prefixed with a backslash.