Add support for -Xshow-phases

[Friendseeker]

Closes #621

Output of -Xshow-phases with the PR

[info] [info]      phase name  id  description
[info] [info]      ----------  --  -----------
[info] [info]          parser   1  parse source into ASTs, perform simple desugaring
[info] [info]           namer   2  resolve names, attach symbols to named trees
[info] [info]  packageobjects   3  load package objects
[info] [info]           typer   4  the meat and potatoes: type the trees
[info] [info]          patmat   5  translate match expressions
[info] [info]  superaccessors   6  add super accessors in traits and nested classes
[info] [info]      extmethods   7  add extension methods for inline classes
[info] [info]         pickler   8  serialize symbol tables
[info] [info]        xsbt-api   9  construct a representation of the public API
[info] [info] xsbt-dependency  10  extract dependency information
[info] [info]       refchecks  11  reference/override checking, translate nested objects
[info] [info]         uncurry  12  uncurry, translate function values to anonymous classes
[info] [info]          fields  13  synthesize accessors and fields, add bitmaps for lazy vals
[info] [info]       tailcalls  14  replace tail calls by jumps
[info] [info]      specialize  15  @specialized-driven class and method specialization
[info] [info]   explicitouter  16  this refs to outer pointers
[info] [info]         erasure  17  erase types, add interfaces for traits
[info] [info]     posterasure  18  clean up erased inline classes
[info] [info]      lambdalift  19  move nested functions to top level
[info] [info]    constructors  20  move field definitions into constructors
[info] [info]         flatten  21  eliminate inner classes
[info] [info]           mixin  22  mixin composition
[info] [info]         cleanup  23  platform-specific cleanups, generate reflective calls
[info] [info]      delambdafy  24  remove lambdas
[info] [info]             jvm  25  generate JVM bytecode
[info] [info]   xsbt-analyzer  26  analyze the generated class files and map them to sources
[info] [info]        terminal  27  the last phase during a compilation run

[eed3si9n]

Thanks!