[Fix] Fixed bug in RSE file loading ( XML-formatted engine description)

This patch is based off a thread from "The Rocketry Forum"
( http://www.rocketryforum.com/showthread.php?70475-Problems-with-custom-motors-in-OpenRocket ) .

Complaint: Poster had a water-rocket engine file which would raise IOExceptions upon automatic load.
           (1) the original .rse motor file, posted in the thread above, has an invalid motor length.
           (2) The corrected .rse file follows at the end of this commit message.
Bug: The mass auto-scaling code would over-estimate the mass loss, and declare a negative mass upon motor exhaustion.
     The negative mass is small (in this case, ~= -1E-16).  However, this error is larger than the single-precision epsilon.
Fix: Added a loop which checked for negative mass during the thrust curve, and reset those values back to zero. (AbstractMotorLoader.java:105)
     Also, expanded the number and detail level of some related exception reporting. (ThrustCurveMotor:137)

----

<engine-database>
  <engine-list>
    <engine  mfg="Water" code="W90psi" Type="single-use" dia="18.001" len="200."
initWt="800." propWt="800." delays="1000" auto-calc-mass="1" auto-calc-cg="0"
avgThrust="280.059" peakThrust="428.329" throatDia="0." exitDia="0."
Itot="21.284" burn-time="0.08" massFrac="99.88" Isp="2.71" tDiv="10" tStep="-1."
tFix="1" FDiv="10" FStep="-1." FFix="1" mDiv="10" mStep="-1." mFix="1" cgDiv="10"
cgStep="-1." cgFix="1">
    <comments>Water Rocket, 90 psi, 800g</comments>
    <data>
      <eng-data  t="0." f="0." m="800." cg="81.6327"/>
      <eng-data  t="0.001" f="428.329" m="791.95" cg="89.1566"/>
      <eng-data  t="0.005" f="405.382" m="729.279" cg="107.229"/>
      <eng-data  t="0.008" f="383.711" m="684.79" cg="115.663"/>
      <eng-data  t="0.016" f="346.742" m="574.971" cg="132.53"/>
      <eng-data  t="0.023" f="319.972" m="487.264" cg="142.169"/>
      <eng-data  t="0.031" f="294.476" m="394.885" cg="154.217"/>
      <eng-data  t="0.041" f="267.705" m="289.234" cg="163.855"/>
      <eng-data  t="0.051" f="244.759" m="192.927" cg="172.289"/>
      <eng-data  t="0.059" f="229.462" m="121.63" cg="178.313"/>
      <eng-data  t="0.067" f="215.439" m="54.742" cg="186.747"/>
      <eng-data  t="0.072" f="203.966" m="15.3326" cg="189.157"/>
      <eng-data  t="0.076" f="0." m="0." cg="192.857"/>
    </data>
  </engine>
</engine-list>
</engine-database>