.jvmopts is parsed differently comparing to the original(*) sbt launcher

The original sbt recognizes spaces within lines of .jvmopts as a property separator whereas sbt-extras does not respect the spaces.

Having both the original sbt v1.7.1 and sbt-extras (installed as sbtx from the current master):

$ mkdir sbtx-vs-sbt-jvmopts
$ cd sbtx-vs-sbt-jvmopts
$ mkdir project
$ echo 'sbt.version=1.7.1' > project/build.properties
$ echo '-Daaa=bbb -Dccc=ddd' > .jvmopts
$ echo 'object TheApp extends App { sys.props.foreach(println) }' > TheApp.scala
Run the app with the original launcher: $ sbt run
Observe that aaa=bbb and ccc=ddd are parsed as separate properties:
```
...
(aaa, bbb)
(ccc, ddd)
...
```
Run the app with sbt-extras: $ sbtx run
Observe that these two parsed as a single property aaa=bbb -Dccc=ddd:
```
...
(aaa,bbb -Dccc=ddd)
...
```

p.7 and p.9 from the above should emit identical sets of system properties including aaa=bbb and ccc=ddd.

The produced results are different, actually.

dwijnand / sbt-extras