Options to exclude maven classpath from gem-maven-plugin:exec

Created by: leonidv

I got createprocess error=206 the filename or extension is too long when try to use gem-maven-plugin in javaee project. It's because we have very many dependencies and windows can't execute process with huge comand line.

For fix this problem I added options to exclude (exactly, it's named add project classpath) to AbstractJRubyMojo.

Example of usage:

            <plugin>
                <groupId>de.saumya.mojo</groupId>
                <artifactId>gem-maven-plugin</artifactId>
                <version>1.0.9-SNAPSHOT</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>exec</goal>
                        </goals>
                        <phase>generate-resources</phase>
                        <configuration>
                            <addProjectClasspath>false</addProjectClasspath>
                            <skipGemInstall>true</skipGemInstall>
                            <execArgs>${gem.home}\bin\compass compile
                                ${basedir}\src\main\sass
                                --sass-dir ${basedir}\src\main\sass\
                                --css-dir ${project.build.directory}\css</execArgs>
                        </configuration>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>rubygems</groupId>
                        <artifactId>compass</artifactId>
                        <version>1.0.3</version>
                        <type>gem</type>
                    </dependency>
                </dependencies>
            </plugin>