Remove extra quotations in batch files

The command

```bat
SET AGAVI_SOURCE_DIRECTORY="@PEAR-DIR@/agavi"
```
actually includes the quotations in the value. This is not desired, and
it resulted in an error when I attempted to run agavi for the first
time.

The error was

```
'""D:\Programs\PHP' is not recognized as an internal or external
command,
operable program or batch file.
```